[LeetCode] 20. Valid Parentheses

• 題目: Valid Parentheses 判斷字串是否為合理的左右括號
• 作法: 實作 First in last out 的 stack, 遇到左括號做 push, 右括號 pop, 若不是對應的括號或是沒有 pop 完, 則不是 valid 

class Solution {
public:
    bool isValid(string s) {
        vector bracketVec;
        for (size_t i = 0; i < s.length(); i++){
            if (s[i] == ')' || s[i] == ']' || s[i] == '}' )
            {
                if (bracketVec.empty())
                    return false;
                else if ( (s[i] == ')' && bracketVec.back() == '(')
                        || (s[i] == ']' && bracketVec.back() == '[')
                        || (s[i] == '}' && bracketVec.back() == '{'))
                    bracketVec.pop_back();
                else
                    return false;
            }
            else if (s[i] == '(' || s[i] == '[' || s[i] == '{')
            {
                bracketVec.push_back(s[i]);
            }
        }

        return bracketVec.empty();
    }
};