leetcode: Valid Parentheses

http://oj.leetcode.com/problems/valid-parentheses/

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.

思路：

用一个堆栈保存左括号然后匹配即可。

class Solution {
public:
    bool isValid(string s) {
        stack<char> left_pars;
        const char *p = s.c_str();
        
        while (*p != '\0') {
            if (('(' == *p) || ('[' == *p) || ('{' == *p)) {
                left_pars.push(*p);
            }
            else {
                if (left_pars.empty()) {
                    return false;
                }
                
                char exp_left_par;
                
                if (')' == *p) {
                    exp_left_par = '(';
                }
                else if (']' == *p) {
                    exp_left_par = '[';
                }
                else {
                    exp_left_par = '{';
                }
                
                if (left_pars.top() == exp_left_par) {
                    left_pars.pop();
                }
                else {
                    return false;
                }
            }
            
            ++p;
        }
        
        return left_pars.empty() ? true : false;
    }
};