add khushal87 longest_valid_paranthesis

Stack/longest_valid_paranthesis.c++

@@ -0,0 +1,42 @@
+#include <bits/stdc++.h>
+using namespace std;
+
+int lengthOfLongestValidParanthesis(string s)
+{
+ int n = s.length();
+ stack<int> st;
+ st.push(-1);
+
+ int result = 0;
+ for (int i = 0; i < n; i++)
+ {
+ if (s[i] == '(')
+ {
+ st.push(i);
+ }
+ else
+ {
+ if (!st.empty())
+ {
+ st.pop();
+ }
+ if (!st.empty())
+ {
+ result = max(result, i - st.top());
+ }
+ else
+ {
+ st.push(i);
+ }
+ }
+ }
+ return result;
+}
+
+int main()
+{
+ string s;
+ cin >> s;
+ int ans = lengthOfLongestValidParanthesis(s);
+ cout << "Length = " << ans << endl;
+}