Find Duplicate in Range 0 and n-1

Code

#include <stdio.h>

int find_duplicate(int arr[], int n) {
    if(n<2) return -1;
    int actual_sum = 0,curr=0;
    int zeroFlag=0;
    for (int i = 0; i < n; i++){
        curr = curr ^ arr[i];
        if(arr[i]==0) zeroFlag=1;
    }
    for (int i = 0; i <n-zeroFlag; i++){
        actual_sum = actual_sum ^ i;
    }
    return actual_sum^curr;
}

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