find the min frequency using linear traversal
int min_count = n + 1 , res = -1 , curr_count = 1 ; for ( int i = 1 ; i < n ; i ++ ) { if ( arr [ i ] == arr [ i - 1 ] ) curr_count ++ ; else { if ( curr_count < min_count ) { min_count = curr_count ; res = arr [ i - 1 ] ; } curr_count = 1 ; } }