137. Single Number II

https://leetcode.com/problems/single-number-ii/description/

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

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

解题思路：
使用HashMap存每个元素出现的次数

import java.util.Map.Entry;

public class Solution {
    public int singleNumber(int[] nums) {
         Map<Integer,Integer> map = new HashMap<Integer,Integer>();
        int result=0;
        for(int i:nums){
            if(!map.containsKey(i)){
                map.put(i, 1);
            }else{
                map.put(i, map.get(i)+1);
            }
        }
        Set<Entry<Integer,Integer>> entrySet = map.entrySet();
        for(Entry es:entrySet){
            int count = (Integer)es.getValue();
            if(count!=3){
                result = (Integer)es.getKey();
                break;
            }
        }
        return result;
    }
}