【LeetCode 20. Valid Parentheses】（合法括号匹配判断，栈的应用）

【LeetCode 20. Valid Parentheses】（合法括号匹配判断，栈的应用）

题目链接 Given a string containing just the characters ‘(‘, ‘)’, ‘{‘, ‘}’, ‘[’ and ‘]’, determine if the input string is valid. An input string is valid if: Open brackets must be closed by the same type of brackets. Open brackets must be closed in the correct order. Note that an empty string is also considered valid. Example 1: Input: “()” Output: true Example 2: Input: “()[]{}” Output: true Example 3: Input: “(]” Output: false Example 4: Input: “([)]” Output: false Example 5: Input: “{[]}” Output: true 题意：给定一个由括号字符组成的字符串，问是否合法。 思路： 最简单的思路，遍历判断入栈，最后判断栈是否为空。 Code： import java.util.Stack; public class Solution { public boolean isValid(String s) { Stack stack = new Stack(); for (char ch : s.toCharArray()) { if (ch == '(') { stack.push(')'); } else if (ch == '[') { stack.push(']'); } else if (ch == '{') { stack.push('}'); } else if (stack.empty() || stack.pop() != ch) {///栈为空或者栈顶不等于ch return false; } } return stack.empty(); } public static void main(String[] args) { String str = "" + "()"; boolean res = new Solution().isValid(str); System.out.println(res); } }

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