32. Longest Valid Parentheses

Author: SjxSubham

32. Longest Valid Parentheses

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+//simple c++ approach
+//T.C- O(n)
+//Stack class 3
+//HARD question
+
+class Solution {
+public:
+    int longestValidParentheses(string s) {
+        stack<int>st;
+        st.push(-1);
+        int maxlen =0;
+        for(int i=0;i<s.length();i++){
+            char ch = s[i];
+            if(ch == '('){
+                st.push(i);
+            }
+            else{
+                st.pop();
+                if(st.empty()) {
+                    st.push(i);  //hard area
+                }
+                else{
+                    int len = i - st.top();
+                    maxlen = max(len,maxlen);
+                }
+            }
+        }
+        return maxlen;
+    }
+};