Find Duplicate in Range 0 and n-1

Code

#include <stdio.h>

int find_duplicate(int arr[], int n) {
    // Your logic here
    int repeating;
    int idx = n;
    while(idx) {
        idx--;
        repeating = arr[idx];
        for(int i = 0; i < n; i++) {
            if (i == idx) {
                continue;
            }
            if (arr[i] == repeating) {
                idx = 0;
                break;
            }
        }
    }
    return repeating;
}

int main() {
    int n;
    scanf("%d", &n);

    int arr[100];
    for (int i = 0; i < n; i++) scanf("%d", &arr[i]);

    int result = find_duplicate(arr, n);
    printf("%d", result);
    return 0;
}

Solving Approach