50212. Bits Swapping

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <stdint.h>
#include <ctype.h>

int cnt_1(int arr[], int start, int finish){
    int cnt = 0;
    for(int i = start; i < finish; i++){
        if(arr[i] == 1) cnt++;
    }
    return cnt;
}


void x(int arr[], int start, int finish){
    if(start + 1 == finish) return;

    int mid = (start + finish) / 2;
    int cnt = cnt_1(arr, start, finish);
    if(cnt % 2 == 1){
        for(int i = start, j = mid; i < mid; i++, j++){
            int t = arr[i];
            arr[i] = arr[j];
            arr[j] = t;
        }
    }

    x(arr, start, mid);
    x(arr, mid, finish);
}

int main(){
    uint32_t n;
    scanf("%u", &n);
    int arr[32] = {0};
    for(int i = 0; i < 32; i++){
        arr[i] = ((n >> 31 - i) & 1);
    }

    x(arr, 0, 32);

    uint32_t f = 0;
    for(int i = 0; i < 32; i++){
        if(arr[i] == 1){
            f |= ((uint32_t)1 << (31 - i));
        }
    }
    printf("%u\n", f);
}