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

An input string is valid if:

  1. Open brackets must be closed by the same type of brackets.
  2. Open brackets must be closed in the correct order.

Note that an empty string is also considered valid.

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

 

简单题。。但是还是看的柳婼的答案过的。。用的 栈hh

class Solution {
public:
    bool isValid(string s) {
        stack<int> 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();
    }
};

 

if(i==0||t.empty()||t.top()!='(')学习这个判断就行了~