[1] Given an array of integers, every element appears twice except for one. Find that single one.[2] Given an array of integers, every element appears three times except for one. Find that single one. (better solution is needed)Note: Your algorithm should have a linear runtime complexity. Could you implement it without using extra memory?

题目中文意思就是说给定一个整数数组，数组中所有元素都出现了两次，只有一个元素只出现了一次，找出这个只出现了一次的元素。

用异或来解决这类问题会非常简单。

代码：

int SingleNumber(int arr[] , int length){    int i , xor;    for(xor = 0 , i = 0 ; i < length ; ++i)        xor = xor ^ arr[i];    return xor;}

完整代码：

1 #include
     
       2 using namespace std; 3  4 int SingleNumber(int arr[] , int length) 5 { 6     int i , xor; 7     for(xor = 0 , i = 0 ; i < length ; ++i) 8         xor = xor ^ arr[i]; 9 10     return xor;11 }12 13 int main()14 {15     int arr[] = {
   2 , 1 , 2 , 1 , 3 , 4 , 3};16     int length = sizeof(arr)/ sizeof(int);17 18     cout<