32. 最长有效括号
作者:互联网
32. 最长有效括号
难度:困难
给你一个只包含 '('
和 ')'
的字符串,找出最长有效(格式正确且连续)括号子串的长度。
示例 1:
输入:s = "(()"
输出:2
解释:最长有效括号子串是 "()"
示例 2:
输入:s = ")()())"
输出:4
解释:最长有效括号子串是 "()()"
示例 3:
输入:s = ""
输出:0
提示:
0 <= s.length <= 3 * 10^4
s[i]
为'('
或')'
解答:
class Solution {
//动态规划
//时间复杂度O(N), 空间复杂度O(N)
public int longestValidParentheses(String s) {
int maxAns = 0;
int[] dp = new int[s.length()];
for(int i = 1; i < s.length(); i++){
if(s.charAt(i) == ')'){
if(s.charAt(i - 1) == '('){
dp[i] = (i >= 2 ? dp[i - 2] : 0) + 2;
}else if(i - dp[i - 1] > 0 && s.charAt(i - dp[i - 1] - 1) == '('){
dp[i] = dp[i - 1] + ((i - dp[i - 1]) >= 2 ? dp[i - dp[i - 1] - 2] : 0) + 2;
}
maxAns = Math.max(dp[i], maxAns);
}
}
return maxAns;
}
}
class Solution {
//栈
//时间复杂度O(N), 空间复杂度O(N)
public int longestValidParentheses(String s) {
int maxAns = 0;
Deque<Integer> stack = new LinkedList<>();
stack.push(-1);
for(int i = 0; i < s.length(); i++){
if(s.charAt(i) == '('){
stack.push(i);
}else{
stack.pop();
if(stack.isEmpty()){
stack.push(i);
}else{
maxAns = Math.max(maxAns, i - stack.peek());
}
}
}
return maxAns;
}
}
class Solution {
//双指针
//时间复杂度O(N), 空间复杂度O(1)
public int longestValidParentheses(String s) {
int maxAns = 0;
int left = 0;
int right = 0;
for(int i = 0; i < s.length(); i++){
if(s.charAt(i) == '(') left++;
else right++;
if(left == right) maxAns = Math.max(maxAns, right * 2);
else if(right > left) left = right = 0;
}
left = right = 0;
for(int i = s.length() - 1; i >= 0; i--){
if(s.charAt(i) == '(') left++;
else right++;
if(left == right) maxAns = Math.max(maxAns, left * 2);
else if(left > right) left = right = 0;
}
return maxAns;
}
}
参考自:
作者:LeetCode-Solution
链接:https://leetcode-cn.com/problems/longest-valid-parentheses/solution/zui-chang-you-xiao-gua-hao-by-leetcode-solution/
来源:力扣(LeetCode)
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标签:right,int,32,maxAns,stack,括号,最长,dp,left 来源: https://blog.csdn.net/qq_37548441/article/details/117918629