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.
使用栈，每匹配一对括号就出栈。最后栈要为空才完全匹配。
class Solution { public: bool isValid(string s) { if(s == "") return true; stack<char> stk; for(int i = 0; i < s.size(); i ++) { switch(s[i]) { case ‘(‘: stk.push(s[i]); break; case ‘)‘: if(!stk.empty() && stk.top() == ‘(‘) stk.pop(); else return false; break; case ‘[‘: stk.push(s[i]); break; case ‘]‘: if(!stk.empty() && stk.top() == ‘[‘) stk.pop(); else return false; break; case ‘{‘: stk.push(s[i]); break; case ‘}‘: if(!stk.empty() && stk.top() == ‘{‘) stk.pop(); else return false; break; default: ; } } if(stk.empty()) return true; else return false; } };
原文：http://www.cnblogs.com/ganganloveu/p/4175213.html