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.
使用动态规划的思想,从后往前求解,遇到“(”,则进行条件推断。
public int longestValidParentheses(String s) {
if (s == null || s.length() == 0 || s.length() == 1) {
return 0;
}
int len = s.length();
int[] num = new int[len];
num[len - 1] = 0;
for (int i = len - 2; i >= 0; i--) {
if (s.charAt(i) == '(') {
int j = i + 1 + num[i + 1];
if (j < len && s.charAt(j) == ')') {
num[i] = num[i + 1] + 2;
if (j + 1 < len) {
num[i] += num[j + 1];
}
}
}
}
int max = 0;
for (int i = 0; i < len; i++) {
if (max < num[i]) {
max = num[i];
}
}
return max;
}