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‎stack_problems/10PrefixEvaluationAndConversion.cpp‎

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#include<iostream>
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#include<stack>
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using namespace std;
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int operation(int val1,int val2,char ch)
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{
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if(ch=='+')
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{
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return val1+val2;
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}
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else if(ch=='-')
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{
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return val1-val2;
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}
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else if(ch=='*')
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{
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return val1*val2;
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}
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else
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{
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return val1/val2;
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}
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}
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void prefixConversion(string s)
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{
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stack<int> val;
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stack<string> in;
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stack<string> post;
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for(int i=s.size()-1;i>=0;i--)
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{
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char ch=s[i];
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if(ch=='+'|| ch=='-' ||ch=='*'|| ch=='/')
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{
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int val1=val.top();
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val.pop();
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int val2=val.top();
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val.pop();
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int ans=operation(val1,val2,ch);
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val.push(ans);
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string in1=in.top();
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in.pop();
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string in2=in.top();
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in.pop();
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string inAns='('+in1+ch+in2+')';
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in.push(inAns);
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string post1=post.top();
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post.pop();
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string post2=post.top();
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post.pop();
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string postAns=post1+post2+ch;
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post.push(postAns);
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}
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else if(ch==' ')
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{
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continue;
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}
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else
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{
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val.push(ch-'0');
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in.push(string(1,ch));
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post.push(string(1,ch));
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}
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}
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cout<<val.top()<<endl;
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cout<<in.top()<<endl;
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cout<<post.top()<<endl;
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}
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int main()
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{
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string s;
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getline(cin,s);
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prefixConversion(s);
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}

‎stack_problems/11CelebrityProblem.cpp‎

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#include<iostream>
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#include<stack>
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using namespace std;
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int celeb(int n,int **ar)
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{
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stack<int>s;
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for(int i=0;i<n;i++)
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{
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s.push(i);
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}
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while(s.size()>=2)
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{
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int i=s.top();
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s.pop();
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int j=s.top();
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s.pop();
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if(ar[i][j]==1) //i knows j --> i can not be celeb.
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{
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s.push(j);
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}
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else
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{ //i does not know j --> j can not be celeb.
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s.push(i);
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}
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}
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int pot=s.top();
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s.pop();
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for(int i=0;i<n;i++)
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{
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if(pot!=i)
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{
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if(ar[i][pot]==0 || ar[pot][i]==1 )
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{
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return 0;
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}
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}
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}
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return pot;
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}
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int main()
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{
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int n;
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cin>>n;
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int **ar=new int*[n];
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for(int i=0;i<n;i++)
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{
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ar[i]=new int[n];
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for(int j=0;j<n;j++)
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{
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cin>>ar[i][j];
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}
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}
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int ans=celeb(n,ar);
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if(ans==0)
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{
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cout<<"none"<<endl;
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}
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else
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cout<<ans<<endl;
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}

‎stack_problems/7InfixEvaluation.cpp‎

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#include<iostream>
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#include<stack>
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using namespace std;
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int precedence(char oprtr)
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{
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if(oprtr=='+')
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{
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return 1;
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}
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else if(oprtr=='-')
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{
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return 1;
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}
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else if(oprtr=='*')
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{
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return 2;
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}
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else
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{
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return 2;
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}
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}
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int operation(int v1,int v2,char oprtr)
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{
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if(oprtr=='+')
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{
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return v1+v2;
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}
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else if(oprtr=='-')
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{
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return v1-v2;
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}
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else if(oprtr=='*')
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{
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return v1*v2;
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}
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else
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{
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return v1/v2;
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}
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}
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int infixEval(string s)
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{
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stack<char> op;
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stack<int> opand;
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for(int i=0;i<s.size();i++)
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{
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char ch=s[i];
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if(ch=='(')
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{
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op.push(ch);
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}
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else if(isdigit(ch))
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{
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opand.push(ch-'0');
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}
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else if(ch==')')
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{
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while(op.top()!='(')
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{
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char oprtr=op.top();
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op.pop();
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int val2=opand.top();
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opand.pop();
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int val1=opand.top();
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opand.pop();
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int ans=operation(val1,val2,oprtr);
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opand.push(ans);
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}
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op.pop();
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}
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else if(ch=='+'|| ch=='-' || ch=='*' || ch=='/')
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{
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while(op.size()>0 && op.top()!='(' && precedence(ch)<=precedence(op.top()))
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{
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char oprtr=op.top();
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op.pop();
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int val2=opand.top();
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opand.pop();
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int val1=opand.top();
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opand.pop();
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int ans=operation(val1,val2,oprtr);
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opand.push(ans);
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}
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op.push(ch);
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}
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else
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{
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continue;
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}
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}
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while(op.size()!=0)
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{
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char oprtr=op.top();
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op.pop();
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int val2=opand.top();
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opand.pop();
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int val1=opand.top();
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opand.pop();
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int ans=operation(val1,val2,oprtr);
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opand.push(ans);
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}
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return opand.top();
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}
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int main()
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{
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string s;
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getline(cin,s);
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int ans=infixEval(s);
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cout<<ans<<endl;
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}

‎stack_problems/8InfixConversion.cpp‎

Lines changed: 112 additions & 0 deletions
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#include<iostream>
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#include<stack>
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using namespace std;
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int precedence(char ch)
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{
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if(ch=='+')
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{
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return 1;
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}
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else if(ch=='-')
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{
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return 1;
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}
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else if(ch=='*')
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{
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return 2;
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}
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else
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{
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return 2;
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}
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}
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void infixConversion(string s)
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{
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stack<char>oprtr;
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stack<string>pre;
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stack<string>post;
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for(int i=0;i<s.size();i++)
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{
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char ch=s[i];
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if(ch=='(')
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{
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oprtr.push(ch);
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}
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else if((ch>='1' && ch<='9') || (ch>='a' && ch<='z' ) || (ch>='A' && ch<='Z'))
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{
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pre.push(string(1,ch));
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post.push(string(1,ch));
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}
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else if(ch==')')
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{
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while(oprtr.top()!='(')
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{
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char op=oprtr.top();
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oprtr.pop();
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string val2=pre.top();
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pre.pop();
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string val1=pre.top();
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pre.pop();
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string val2Post=post.top();
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post.pop();
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string val1Post=post.top();
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post.pop();
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string prefix=op+val1+val2;
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string postfix=val1Post+val2Post+op;
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pre.push(prefix);
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post.push(postfix);
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}
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oprtr.pop();
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}
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else
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{
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if(oprtr.size()>0 && oprtr.top()!='(' && precedence(ch)<=precedence(oprtr.top()))
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{
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char op=oprtr.top();
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oprtr.pop();
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string val2=pre.top();
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pre.pop();
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string val1=pre.top();
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pre.pop();
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string val2Post=post.top();
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post.pop();
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string val1Post=post.top();
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post.pop();
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string prefix=op+val1+val2;
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string postfix=val1Post+val2Post+op;
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pre.push(prefix);
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post.push(postfix);
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}
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oprtr.push(ch);
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}
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}
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while(oprtr.size()!=0)
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{
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char op=oprtr.top();
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oprtr.pop();
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string val2=pre.top();
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pre.pop();
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string val1=pre.top();
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pre.pop();
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string val2Post=post.top();
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post.pop();
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string val1Post=post.top();
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post.pop();
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string prefix=op+val1+val2;
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string postfix=val1Post+val2Post+op;
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pre.push(prefix);
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post.push(postfix);
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}
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cout<<pre.top()<<endl;
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cout<<post.top()<<endl;
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}
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int main()
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{
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string s;
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getline(cin,s);
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infixConversion(s);
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}

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