[LeetCode]Valid Parentheses

题目描述:(链接)

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.

解题思路:

用一个stack实现

class Solution {
public:
    bool isValid(string s) {
        for (int i = 0; i < s.size(); ++i) {
            switch (s[i]) {
                case '(':
                case '{':
                case '[': {
                    cache.push(s[i]); 
                    break;
                }
                case ')': {
                    if (!isSuitable('(')) {
                        return false;
                    }
                    break;
                }
                case '}': {
                    if (!isSuitable('{')) {
                        return false;
                    }
                    break;
                }
                case ']': {
                    if (!isSuitable('[')) {
                        return false;
                    }
                    break;
                }
            }
        }
        
        if (!cache.empty()) return false;
        
        return true;
    }
private:
    stack<int> cache;
    bool isSuitable(int character) {
        if (cache.empty()) {
            return false;
        }
        
        int ch = cache.top();
        if (ch != character) {
            return false;
        }
        
        cache.pop();
        
        return true;
    }
};