Create 32.cpp

LeetCode-CN/32.cpp

@@ -0,0 +1,43 @@
+#include <algorithm>
+#include <stack>
+class Solution {
+public:
+    int longestValidParentheses(string s) {
+        int len = s.size();
+        int maxp = 0;
+        stack<int> stk;
+
+        for (int i = 0; i < len; i++)
+        {
+            if (s[i] == '(')
+            {
+                stk.push(i);
+            }
+            else // if (s[i] == ')')
+            {
+                // Stack not empty, and symbol matches.
+                if (!stk.empty() && s[stk.top()]=='(')
+                {
+                    // Pop matched pairs.
+                    stk.pop();
+                    if (stk.empty())
+                    {
+                        // From Start to i is a valid string.
+                        maxp = std::max(i + 1, maxp);
+                    }
+                    else
+                    {
+                        // From stk.top()+1 to i is a valid string. Length: i-(stk.top()+1)+1
+                        maxp = std::max(i - stk.top(), maxp);
+                    }
+                }
+                else
+                {
+                    // new start point (stub)
+                    stk.push(i);
+                }
+            }
+        }
+        return maxp;
+    }
+};