LeetCode--[栈]--不定时更新

1.1链接

https://leetcode-cn.com/problems/valid-parentheses/

1.2题目描述

 

 

 1.3解决思路

 

 

 1.4代码实现

java版本

import java.util.HashMap;
import java.util.Stack;

public class _20_有效的括号 {
    private static HashMap<Character, Character> map = new HashMap<>();
    static {
        // key - value
        map.put('(', ')');
        map.put('{', '}');
        map.put('[', ']');
    }
    
    public boolean isValid(String s) {
        Stack<Character> stack = new Stack<>();
        
        int len = s.length();
        for (int i = 0; i < len; i++) {
            char c = s.charAt(i);
            if (map.containsKey(c)) { // 左括号
                stack.push(c);
            } else { // 右括号
                if (stack.isEmpty()) return false;
                
                if (c != map.get(stack.pop())) return false;
            }
        }
        return stack.isEmpty();
    }
    
    public boolean isValid1(String s) {
        Stack<Character> stack = new Stack<>();
        
        int len = s.length();
        for (int i = 0; i < len; i++) {
            char c = s.charAt(i);
            if (c == '(' || c == '{' || c == '[') { // 左括号
                stack.push(c);
            } else { // 右括号
                if (stack.isEmpty()) return false;
                
                char left = stack.pop();
                if (left == '(' && c != ')') return false;
                if (left == '{' && c != '}') return false;
                if (left == '[' && c != ']') return false;
            }
        }
        return stack.isEmpty();
    }

    public boolean isValid2(String s) {
        while (s.contains("{}")
                || s.contains("[]")
                || s.contains("()")) {
            s = s.replace("{}", "");
            s = s.replace("()", "");
            s = s.replace("[]", "");
        }
        return s.isEmpty();
    }
    
}

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