[LeetCode] 20. Valid Parentheses 驗證括號

 

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

 

這道題讓咱們驗證輸入的字符串是否爲括號字符串，包括大括號，中括號和小括號。這裏須要用一個棧，開始遍歷輸入字符串，若是當前字符爲左半邊括號時，則將其壓入棧中，若是遇到右半邊括號時，若此時棧爲空，則直接返回 false，如不爲空，則取出棧頂元素，若爲對應的左半邊括號，則繼續循環，反之返回 false，代碼以下：

 

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

 

Github 同步地址：

https://github.com/grandyang/leetcode/issues/20

 

相似題目：

Remove Invalid Parentheses

Different Ways to Add Parentheses

Longest Valid Parentheses

Generate Parentheses

Check If Word Is Valid After Substitutions

 

參考資料：

https://leetcode.com/problems/valid-parentheses/

https://leetcode.com/problems/valid-parentheses/discuss/9178/Short-java-solution

https://leetcode.com/problems/valid-parentheses/discuss/9248/My-easy-to-understand-Java-Solution-with-one-stack

 

LeetCode All in One 題目講解彙總(持續更新中...)