136.Single Number （数组中只出现一次的数）

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

代码：

public class Solution {
    public int singleNumber(int[] nums) {
        HashMap<Integer, Integer> map = new HashMap<>(); 
    for(int i=0;i<nums.length;i++){
    if(!map.containsKey(nums[i])){
    map.put(nums[i], 1);
    }else{
    int count = map.get(nums[i])+1;
    map.put(nums[i], count);
    }
    }
   
    Iterator<Integer> iter = map.keySet().iterator();
    while(iter.hasNext()){
    int key = iter.next();
    if(map.get(key)==1){
    return key;
    }
    }
    return 0;
    }
}