LeetCode 20. Valid Parentheses

Given a string containing just the characters ‘(‘, ‘)’, ‘{‘, ‘}’, ‘[‘ and ‘]’, determine if the input string is valid.

The brackets must close in the correct order, “()” and “()[]{}” are all valid but “(]” and “([)]” are not.

class Solution {
public:
    bool isValid(string s) {
        stack<char> t;
        for(int i = 0; i < s.length(); i++) {
            if(s[i] == '(' || s[i] == '[' || s[i] == '{') {
                t.push(s[i]);
            } else if(s[i] == ')') {
                if(i == 0 ||  t.empty() || t.top() != '(') {
                    return false;
                }
                t.pop();
            } else if(s[i] == ']') {
                if(i == 0 || t.empty() || t.top() != '[') {
                    return false;
                }
                t.pop();
            } else if(s[i] == '}') {
                if(i == 0 || t.empty() || t.top() != '{') {
                    return false;
                }
                t.pop();
            }
        }
        return t.empty();
    }
};

class Solution {

public:

bool isValid(string s) {

stack<char> t;

for(int i = 0; i < s.length(); i++) {

if(s[i] == '(' || s[i] == '[' || s[i] == '{') {

t.push(s[i]);

} else if(s[i] == ')') {

if(i == 0 || t.empty() || t.top() != '(') {

return false;

}

t.pop();

} else if(s[i] == ']') {

if(i == 0 || t.empty() || t.top() != '[') {

return false;

}

t.pop();

} else if(s[i] == '}') {

if(i == 0 || t.empty() || t.top() != '{') {

return false;

}

t.pop();

}

return t.empty();

}

};

❤ 点击这里 -> 订阅《PAT | 蓝桥 | LeetCode学习路径 & 刷题经验》by 柳婼

❤ 点击这里 -> 订阅《从放弃C语言到使用C++刷算法的简明教程》by 柳婼

❤ 点击这里 -> 订阅PAT甲级乙级、蓝桥杯、GPLT天梯赛、LeetCode题解离线版