Valid Substring

Author: sachuverma

DSA Crack Sheet/README.md

@@ -157,6 +157,7 @@
 - [Sort a stack](https://practice.geeksforgeeks.org/problems/sort-a-stack/1# "view question") - [Cpp Solution](./solutions/Sort%20a%20stack.cpp)
 - [Merge Intervals](https://leetcode.com/problems/merge-intervals/ "view question") - [Cpp Solution](./solutions/Merge%20Intervals.cpp)
 - [Maximum Rectangular Area in a Histogram](https://practice.geeksforgeeks.org/problems/maximum-rectangular-area-in-a-histogram-1587115620/1 "view question") - [Cpp Solution](./solutions/Maximum%20Rectangular%20Area%20in%20a%20Histogram.cpp)
+- [Valid Substring](https://practice.geeksforgeeks.org/problems/valid-substring0624/1# "view question") - [Cpp Solution](./solutions/Valid%20Substring.cpp)
 - []( "view question") - [Cpp Solution](./solutions/.cpp)
 
 ### Heap

DSA Crack Sheet/solutions/Valid Substring.cpp

@@ -0,0 +1,54 @@
+/*
+Valid Substring
+===============
+
+Given a string S consisting only of opening and closing parenthesis 'ie '('  and ')', find out the length of the longest valid(well-formed) parentheses substring.
+NOTE: Length of smallest the valid substring ( ) is 2.
+
+Example 1:
+Input: S = "(()("
+Output: 2
+Explanation: The longest valid 
+substring is "()". Length = 2.
+
+Example 2:
+Input: S = "()(())("
+Output: 6
+Explanation: The longest valid 
+substring is "()(())". Length = 6.
+
+Your Task:  
+You dont need to read input or print anything. Complete the function findMaxLen() which takes S as input parameter and returns the maxlength.
+
+Expected Time Complexity:O(n)
+Expected Auxiliary Space: O(1)   
+
+Constraints:
+1 <= |S| <= 105
+*/
+
+int findMaxLen(string s)
+{
+  stack<int> si;
+  si.push(-1);
+
+  int ans = 0;
+
+  for (int i = 0; i < s.size(); ++i)
+  {
+    if (s[i] == '(')
+      si.push(i);
+    else
+    {
+      si.pop();
+      if (si.size())
+      {
+        int curr = i - si.top();
+        ans = max(ans, curr);
+      }
+      else
+        si.push(i);
+    }
+  }
+  return ans;
+}