Valid Parentheses (Easy)

Description:

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.

Analysis:

括号匹配,用栈模拟就可以了～

My Solution

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
//C++
class Solution {
public:
    bool isValid(string s){
    stack<char> ft;
    for(int i=0;i<(int)s.length();i++){
        if(s[i]=='('||s[i]=='['||s[i]=='{')
            ft.push(s[i]);
        else{
            if(ft.empty())
                return false;
            if(s[i]==')'){
                if(ft.top()=='(')
                    ft.pop();
                else{
                    return false;
                }
            }
            else if(s[i]==']'){
                if(ft.top()=='[')
                    ft.pop();
                else
                    return false;
            }
            else if(s[i]=='}'){
                if(ft.top()=='{')
                    ft.pop();
                else
                    return false;
            }
        }
    }
    return (int)ft.size()==0;
    }
};