20. 有效的括号

20. 有效的括号

栈的应用

class Solution {
    public boolean isValid(String s) {
        Deque<Character> stack = new ArrayDeque<>();
        for(char c : s.toCharArray()){
            if(c == '(' || c == '[' || c == '{') stack.push(c);
            else{
                if(!stack.isEmpty() && stack.peek() == map(c)) stack.pop();
                else return false;
            }
        }
        return stack.isEmpty();
    }

    char map(char c){
        if(c == ')') return '(';
        if(c == ']') return '[';
        if(c == '}') return '{';
        return ' ';
    }
}