LeetCode--20. 有效的括號

遍歷字符串的每個字符，是左括號就入棧，是右括號就與棧頂元素進行匹配

import java.util.Stack;

class Solution {
    public boolean isValid(String s) {
        if (s.length() == 0) return true;
        Stack<Character> stack = new Stack<>();
        for (int i = 0; i < s.length(); i++) {
            char c = s.charAt(i);
            if ((c == ')' || c == ']' || c == '}') && stack.isEmpty()) {
                return false;
            }
            if (c == ')' && stack.pop() != '(') {
                return false;
            }
            if (c == ']' && stack.pop() != '[') {
                return false;
            }
            if (c == '}' && stack.pop() != '{') {
                return false;
            }
            if (c == '(' || c == '[' || c == '{') {
                stack.push(c);
            }
        }
        return stack.isEmpty();
    }
}