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：
1 class Solution { 2 public: 3 bool isValid(string s) { 4 if(!s.size()) 5 return true; 6 char c; 7 stack<char> stk; 8 for(int i = 0; i < s.size(); ++i){ 9 if(s[i] == '[' || s[i] == '{' || s[i] == '('){ 10 stk.push(s[i]); 11 continue; 12 }else if(s[i] == ']'){ 13 if(stk.empty()) 14 return false; 15 c = stk.top(); 16 stk.pop(); 17 if(c != '[') 18 return false; 19 }else if(s[i] == '}'){ 20 if(stk.empty()) 21 return false; 22 c = stk.top(); 23 stk.pop(); 24 if(c != '{') 25 return false; 26 }else{ 27 if(stk.empty()) 28 return false; 29 c = stk.top(); 30 stk.pop(); 31 if(c != '(') 32 return false; 33 } 34 } 35 if(stk.empty()) 36 return true; 37 return false; 38 } 39 };
简单一点的话可以使用下面这种方式：
1 bool ValidParentheses(string s) 2 { 3 if (!s.size()) 4 return true; 5 stack<char> stk; 6 map<char, char> m; 7 m['('] = ')'; 8 m['['] = ']'; 9 m['{'] = '}'; 10 for (auto c : s){ 11 if (c == '(' || c == '[' || c == '{'){ 12 stk.push(c); 13 } 14 else if (c == ')' || c == ']' || c == '}'){ 15 if (stk.empty()) 16 return false; 17 if (c == m[stk.top()]) 18 stk.pop(); 19 else 20 return false; 21 } 22 } 23 if (stk.empty()) 24 return true; 25 return false; 26 }
java版本代码如下所示：
1 public class ValidParentheses { 2 public static void main(String[] args) { 3 // TODO Auto-generated method stub 4 ValidParentheses validParentheses = new ValidParentheses(); 5 String string = new String("[]{}(){[]}"); 6 System.out.println("" + validParentheses.ValidParentheses(string)); 7 } 8 9 boolean ValidParentheses(String str){ 10 if(str.length() == 0) 11 return true; 12 Stack<Character> stk = new Stack<Character>(); 13 char [] parentheses = str.toCharArray(); 14 for(char c : parentheses){ 15 if(c == '(' || c == '{' || c == '['){ 16 stk.push(c); 17 }else if(c == ')'){ 18 if(stk.empty() || stk.pop() != '(') 19 return false; 20 }else if(c == '}'){ 21 if(stk.empty() || stk.pop() != '{') 22 return false; 23 }else if(c == ']'){ 24 if(stk.empty() || stk.pop() != '[') 25 return false; 26 } 27 } 28 if(stk.empty()) 29 return true; 30 return false; 31 } 32 }