If the stack becomes empty after popping, push the current index onto the stack to mark the new base position for valid substrings. We can use a stack to keep track of indices of the parentheses. We ...
Given a string containing just the characters '(' and ')', find the length of the longest valid (well-formed) parentheses substring. Example 1: Input: "(()" Output: 2 Explanation: The longest valid ...
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