Create Evaluate_Reverse_Polish_Notation.cc

Author: iphkwan

Evaluate_Reverse_Polish_Notation.cc

@@ -0,0 +1,30 @@
+class Solution {
+public:
+    int evalRPN(vector<string> &tokens) {
+        stack<int> st;
+        int x, y;
+        for (int i = 0; i < tokens.size(); i++) {
+            if ((tokens[i][0] >= '0' && tokens[i][0] <= '9') || (tokens[i].length() > 1)) {
+                x = 0;
+                int j = 0;
+                if (tokens[i][0] == '-')    j++;
+                for (; j < tokens[i].length(); j++)
+                    x = x * 10 + (tokens[i][j] - '0');
+                if (tokens[i][0] == '-')    x = -x;
+                st.push(x);
+            } else {
+                if (st.size() < 2)  return ERROR_CODE;
+                x = st.top(), st.pop();
+                y = st.top(), st.pop();
+                if (tokens[i][0] == '+') st.push(x + y);
+                else if (tokens[i][0] == '-')    st.push(y - x);
+                else if (tokens[i][0] == '*')    st.push(y * x);
+                else if (tokens[i][0] == '/' && x != 0)  st.push(y / x);
+                else    return ERROR_CODE;
+            }
+        }
+        return st.empty() ? 0 : st.top();
+    }
+private:
+    int ERROR_CODE = -1;
+};