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 ...

//Runtime: 60 ms, faster than 11.39% of C++ online submissions for Minimum Remove to Make Valid Parentheses. //Memory Usage: 11.1 MB, less than 100.00% of C++ online submissions for Minimum Remove to ...