[leetcode]Valid Parentheses

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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.

 

演算法思路：

很經典的棧問題，我採用了大量的資料結構，以保證

代碼如下：

 1 public class Solution { 2     public boolean isValid(String s) { 3         if(s == null || (s.length() & 1 )== 1) return false; 4         Set<Character> leftSet = new HashSet<Character>(); 5         Set<Character> rightSet = new HashSet<Character>(); 6         char[] left = {‘(‘,‘[‘,‘{‘}; 7         char[] right = {‘)‘,‘]‘,‘}‘}; 8         Map<Character,Character> pair = new HashMap<Character,Character>(); 9         for(int i = 0; i < left.length;leftSet.add(left[i]),pair.put(left[i], right[i++]));10         for(int i = 0; i < right.length;rightSet.add(right[i++]));11         Stack<Character> stack = new Stack<Character>();12         for(int i = 0; i < s.length(); i++){13             char c = s.charAt(i);14             if(leftSet.contains(c)) {15                 stack.push(c);16             }else if(rightSet.contains(c)){17                 if(stack.isEmpty() || c != pair.get(stack.pop()) ) return false; 18             }19         }20          return stack.isEmpty();21     }22 }

其實完全木有必要，但是我學的資料結構還是多用比較好