LeetCode OJ：Valid Parentheses（有效括号）

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.

简单的堆栈问题，代码如下：

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

简单一点的话可以使用下面这种方式：

 bool ValidParentheses(string s)
 {
     if (!s.size())
         return true;
     stack<char> stk;
     map<char, char> m;
     m['('] = ')';
     m['['] = ']';
     m['{'] = '}';
     for (auto c : s){
         if (c == '(' || c == '[' || c == '{'){
             stk.push(c);
         }
         else if (c == ')' || c == ']' || c == '}'){
             if (stk.empty())
                 return false;
             if (c == m[stk.top()])
                 stk.pop();
             else
                 return false;
         }
     }
     if (stk.empty())
         return true;
     return false;
 }

java版本代码如下所示：

 public class ValidParentheses {
     public static void main(String[] args) {
         // TODO Auto-generated method stub
         ValidParentheses validParentheses = new ValidParentheses();
         String string = new String("[]{}(){[]}");
         System.out.println("" + validParentheses.ValidParentheses(string));
     }

     boolean ValidParentheses(String str){
         if(str.length() == 0)
             return true;
         Stack<Character> stk = new Stack<Character>();
         char [] parentheses = str.toCharArray();
         for(char c : parentheses){
             if(c == '(' || c == '{' || c == '['){
                 stk.push(c);
             }else if(c == ')'){
                 if(stk.empty() || stk.pop() != '(')
                     return false;
             }else if(c == '}'){
                 if(stk.empty() || stk.pop() != '{')
                     return false;
             }else if(c == ']'){
                 if(stk.empty() || stk.pop() != '[')
                     return false;
             }
         }
         if(stk.empty())
             return true;
         return false;
     }
 }