leetcode13.singleNumber

问题描述：

Given an array of integers, every element appears three times except for one. Find that single one.

Note:
Your algorithm should have a linear runtime complexity. Could you implement it without using extra memory?

java代码：

package leetcode11.SingleNumber;

import java.util.Hashtable;
import java.util.Set;

public class Solution {
	
	public static void main(String []args){
		int []a={1,1,1,3,2,3,3};
		System.out.print(singleNumber(a));
	}
	
	public static int singleNumber(int []a){
		Hashtable<Integer,Integer>ht =new Hashtable<Integer,Integer>();
		for(int i=0;i<a.length;i++){
			Integer val=ht.get(a[i]);
			if(val!=null){
				ht.put(a[i], val+1);
			}else
				ht.put(a[i], 1);
		}
		
		Set<Integer> set=ht.keySet();
		for(Integer i:set){
			if(ht.get(i)!=3)
				return i;
		}
		return 0;
	}
	
}

总结：利用Hashtable，记录给定数组，并且记录其出现的次数，利用集合类判断结果