20. Valid Parentheses

Posted 2021-02-15 forprometheus-jun

description:

check whether the (){}[] is valid(is pair)
Note:

Example:

Example 1:

Input: "()"
Output: true
Example 2:

Input: "()[]{}"
Output: true
Example 3:

Input: "(]"
Output: false
Example 4:

Input: "([)]"
Output: false
Example 5:

Input: "{[]}"
Output: true

my answer:

感恩

my answer

一眼想到堆栈，奈何堆栈没有想起我，堆栈的用法get一下ok吧...

大佬的answer：

class Solution {
public:
    bool isValid(string s) {
        stack<char> res;
        for(int i = 0; i < s.size(); ++i){
            if(s[i] == '(' || s[i] == '[' || s[i] == '{') res.push(s[i]);
            else{
                if(res.empty()) return false;
                if(s[i] == ')' && res.top() != '(')return false;
                if(s[i] == ']' && res.top() != '[')return false;
                if(s[i] == '}' && res.top() != '{')return false;
                res.pop();
            }
        }
        return res.empty();
    }
};

relative point get√：

stackres; //definite a stack
stack.top(); // the element on the top of the stack
stack.push(xxx); // push a element on the top of the stack
stack.pop(); // pop the element on the top of the stack
stack.empty();

hint :