Create 402-Remove-K-Digits.cpp

Author: nehalalifayed

cpp/402-Remove-K-Digits.cpp

@@ -0,0 +1,37 @@
+// Time Complexity is O(N) where N is the size of the input string.
+// Space complexity is O(N) as well
+class Solution {
+public:
+    string removeKdigits(string num, int k) {
+      int n = num.size();
+      
+      stack<char>s;
+      int count = k;
+      
+      for(int i = 0 ; i < n; i++)
+      {
+        while(!s.empty() && count > 0 && s.top() > num[i])
+        {
+          s.pop();
+          count--;
+        }
+        s.push(num[i]);
+      }
+      
+      // In case the num was already in a non increasing order (e.x: 123456)
+      while(s.size() != n - k) s.pop();
+     
+      string res = "";
+      while(!s.empty())
+      {
+        res += s.top();
+        s.pop();
+      }
+      reverse(res.begin() , res.end());
+      // Remove the zeros from the left if they exist.
+      while (res[0] == '0') res.erase(0 , 1);
+    
+      
+      return (res == "") ? "0": res;
+    }
+};