Find Duplicate in Range 0 and n-1

Code

#include <stdio.h>

int find_duplicate(int a[], int n) {
    // Your logic here
    int flag=0,i;
    for( i=0;i<n;i++)
    {
        for(int j=i+1;j<n;j++)
        {
            if(a[i]=a[j])
            flag=1;
        }
       if(flag==1)
       break;
    }
    return a[i];
    
}

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