137. Single Number II java solutions

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?

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 1 public class Solution {
 2     public int singleNumber(int[] nums) {
 3         int[] bitcnt = new int[32];
 4         int ans = 0;
 5         for(int i = 0; i< 32;i++){
 6             for(int n : nums){
 7                 if(((n >> i) & 1) == 1){
 8                     bitcnt[i]++;
 9                 }
10             }
11             ans |= (bitcnt[i]%3) << i;
12         }
13         return ans;
14     }
15 }

平常位运算使用的太少了，本题可以用map解决，也可以使用异或运算解决。参见其他大牛的帖子：

http://www.cnblogs.com/springfor/p/3870863.html

http://blog.csdn.net/derrantcm/article/details/47745445