Longest Valid Parentheses
Given a string containing just the characters '('
and ')'
, find the length of the longest valid (well-formed) parentheses substring.
For "(()"
, the longest valid parentheses substring is "()"
, which has length = 2.
Another example is ")()())"
, where the longest valid parentheses substring is "()()"
, which has length = 4.
Analyse: Consider scan the string from two sides.
Runtime: 8ms
1 class Solution { 2 public: 3 int longestValidParentheses(string s) { 4 if(s.size() <= 1) return 0; 5 6 int answer = 0, start = -1, depth = 0; 7 8 for(int i = 0; i < s.size(); i++){ 9 if(s[i] == '(') depth++; 10 else{ 11 depth--; 12 if(depth < 0){ 13 start = i; 14 depth = 0; 15 } 16 else if(depth == 0) answer = max(answer, i - start); 17 } 18 } 19 20 depth = 0; 21 start = s.size(); 22 for(int i = s.size() - 1; i >= 0; i--){ 23 if(s[i] == ')') depth++; 24 else{ 25 depth--; 26 if(depth < 0){ 27 depth = 0; 28 start = i; 29 } 30 else if(depth == 0) answer = max(answer, start - i); 31 } 32 } 33 return answer; 34 } 35 };