Find the position of the kth element in the interval in which it lies
int x = k - total [ index - 1 ] ; while ( l <= h ) { int m = ( l + h ) / 2 ; if ( ( m - L [ index - 1 ] ) + 1 == x ) { return m ; } else if ( ( m - L [ index - 1 ] ) + 1 > x ) h = m - 1 ; else l = m + 1 ; } }