错误代码：
1 #include<iostream> 2 3 using namespace std; 4 5 int longestValidParentheses(string s) 6 { 7 int i = 0; 8 int L = s.length(); 9 int j; 10 int max = 0; 11 while (i < L) 12 { 13 int left = 0; 14 int right = 0; 15 if (s[i] == '(') 16 { 17 left++; 18 j = i + 1; 19 int index = i-1; 20 while (j<L&&left >= right) 21 { 22 if (left == right) 23 index = j-1; 24 if (s[j] == '(') 25 left++; 26 else 27 right++; 28 j++; 29 } 30 if (right >= left) 31 { 32 if (left*2>max) 33 max = left * 2; 34 i = j; 35 } 36 else 37 { 38 if (index == i - 1) 39 ; 40 else 41 { 42 int leftSum = index - i + 1; 43 int rightSum = j - i - (left - right) - leftSum; 44 if (leftSum > max) 45 max = leftSum; 46 if (rightSum > max) 47 max = rightSum; 48 if (leftSum > rightSum) 49 i = index; 50 else 51 i = j; 52 } 53 } 54 } 55 i++; 56 } 57 return max; 58 } 59 60 int main() 61 { 62 string s = "(()(((()"; 63 cout << longestValidParentheses(s) << endl; 64 }
这个题目是一个一维动态规划问题：
参考自：http://blog.csdn.net/a83610312/article/details/8639790
代码：
1 #include<iostream> 2 3 using namespace std; 4 5 int longestValidParentheses(string s) 6 { 7 int L = s.length(); 8 int *flag = new int[L+1]; 9 memset(flag, 0, sizeof(int)*L); 10 int i = L; 11 while (i >= 0) 12 { 13 if (s[i] == '(') 14 { 15 int j = i + 1; 16 while (j < L&&flag[j]>0) 17 j = flag[j] + 1; 18 if (s[j] == ')') 19 flag[i] = j; 20 else 21 flag[i] = -1; 22 } 23 i--; 24 } 25 int max = 0; 26 i = 0; 27 while (i < L) 28 { 29 int j = i; 30 while (j<L&&flag[j] > 0) 31 { 32 j = flag[j] + 1; 33 } 34 if (j - i > max) 35 max = j - i; 36 i = j + 1; 37 } 38 return max; 39 } 40 41 int main() 42 { 43 string s = ")()())"; 44 cout << longestValidParentheses(s) << endl; 45 return 0; 46 }
这里面主要说一下，16~21行。这里的方式是先寻找位置，在判断。这种方法很很好比遍寻找边判断要简单更省时间。