#include <stdio.h>                                                                                                                                            
                                                                                                                                                              
int singleNumber(int* nums, int numsSize) {                                                                                                                   
    int n = 0;                                                                                                                                                
    int i;                                                                                                                                                    
    for (i = 0; i < numsSize; i++) {                                                                                                                          
        n ^= nums[i];                                                                                                                                         
    }                                                                                                                                                         
    return n;                                                                                                                                                 
}                                                                                                                                                             
                                                                                                                                                              
int main() {                                                                                                                                                  
    int nums[] = {1, 1, 2, 2, 3, 4, 4, 5, 5};                                                                                                                 
    printf("%d\n", singleNumber(nums, (int)sizeof(nums)/sizeof(int)));                                                                                        
}