Pattern Generator

문제

Write a program that repeatedly reads two numbers n and k and prints all bit patterns of length n with k ones in descending order (when the bit patterns are considered as binary numbers). 

입력

You may assume that 30 ≥ n > 0, 8 > k ≥ 0, and n ≥ k. The first number in the input gives the number of pairs n and k. The numbers n and k are separated by a single space. Leading zeroes in a bit pattern should be included. See the example below.