**Problem:**

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

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

**Example :**

```
Input : [1 2 2 3 1]
Output : 3
```

**Solution:**

Given an array of integers, every element appears twice except for one. Find that single one. We can use XOR operation. Because every number XOR itself, the results will be zero. So We XOR every integer in the array, and the result is the single one we want to find. Here is the java version code:

```
public class Solution {
public int singleNumber(int[] A) {
int res=0;
for(int i=0;i<A.length;i++){
res=res^A[i];
}
return res;
}
}
```