Verifique los duplicados C
//Array and variables
int arr[] = {6,7,8,2,7};
//each digit goes from 0-9
int seen[10] = {0};
int i,j;
for(i = 0,j = (sizeof(arr) / sizeof(int)) ;i < j;i++,j--)
{
if(++seen[arr[i]] >= 2 || ++seen[arr[j]] >= 2){
printf("Yes \n");
break;
}
}
Ricardo Fonseca