Find a number that appears only once in an array where other numbers appear k times

Find a number that appears only once in an array where other numbers appear k times

Title description

Given an integer array arr and an integer k greater than 1. It is known that only one number appears once in arr, and the other numbers appear k times. Please return the number that appears once.

Enter a description:

The input contains two lines, the first line contains two integers n and k, $1<=n<=10^5,1<k<=100$ , n represents the length of the array arr, and the n integers in the second row represent the array arr. Each number in the array arr is a 32-bit integer.

Output description:

Output an integer, representing the only number that appears once.

Example 1

enter

7 3
5 4 1 1 5 1 5

Output

4

---

answer:

If k identical k-ary numbers are added without carry, the result of the addition must be a k-ary number with 0 in each digit. So we can directly add each bit in the k-ary of each element without carry, and the final result is the element that appears once.

Code:

#include <cstdio>

using namespace std;

int n, k;

int bit[32];

int main(void) {
    
    
    scanf("%d%d", &n, &k);
    int val, idx;
    int up = 0;
    while ( n-- ) {
    
    
        scanf("%d", &val);
        idx = 0;
        while ( val ) {
    
    
            bit[ idx ] += val % k;
            bit[ idx ] %= k;
            val /= k;
            ++idx;
        }
        if ( idx > up ) up = idx;
    }
    int ret = 0;
    for ( int i = up - 1; i >= 0; --i )
        ret = ret * k + bit[ i ];
    return 0 * printf( "%d\n", ret );
}