Java valid parentheses

topic:

Given a string that only includes'(',')','{','}','[',']', judge whether the string is valid.

A valid string must meet:

1. An empty string can be considered a valid string.
2. The left and right brackets must be closed in the correct order.

Such as:

Legal: {[]}()
Illegal: {[}]

**

Implementation code:

**
Method 1:

	// 多次循环替换括号，如果替换后的字符串还是替换前的字符串，则为无效字符串
    public static boolean isValid(String s) {
    
    
        String str="";
        while(!s.equals("")){
    
    
            str=s.replace("{}","").replace("[]","").replace("()","");
            if(s==str){
    
    
                return false;
            }
            s=str;
        }
        return true;
    }

Method 2:

	// 遇到一个正向括号，将对应的反向括号填入栈中
    // 遇到反向括号，将栈中的正向括号拿出比较
    public static boolean isValid1(String s) {
    
    
        Stack<Character> stack = new Stack<Character>();
        for(char c: s.toCharArray()){
    
    
            if(c=='(')stack.push(')');
            else if(c=='[')stack.push(']');
            else if(c=='{')stack.push('}');
            else if(stack.isEmpty()||c!=stack.pop())return false;
        }
        return stack.isEmpty();
    }