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20. Valid Parentheses

2024-08-30 14:09:38   218人阅读

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.

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分析：

遇到‘(‘, ‘{‘, ‘[‘ 就入栈，遇到‘)‘, ‘}‘, ‘]‘ 就和栈顶元素进行对比，相同则继续，不同返回false
其他false情形：
当对比时，栈已经empty了

代码

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class Solution {
public:
    bool isValid(string s) {
        stack<char> stk;
        int len = s.size();
        if(0 >= len) return false;
        for(int i = 0; i < len; ++i){
            if(s[i] == ‘(‘ || s[i] == ‘[‘ || s[i] == ‘{‘){
                stk.push(s[i]);
            }
            else{
               if(stk.empty()){
                   return false;
               }
               else{
                   if(match(stk.top(),s[i])){
                       stk.pop();
                   }
                   else{
                       return false;
                   }
               }
            }
        }
        if(stk.empty())
            return true;
        else 
            return false;
    }
    bool match(char c1, char c2){
        switch(c1){
            case ‘(‘:
            return c2 == ‘)‘;
            case ‘{‘:
            return c2 == ‘}‘;
            case ‘[‘:
            return c2 ==‘]‘;
            default:
            return false;
        }
    }
};

来源： http://tool.oschina.net/highlight


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20. Valid Parentheses


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