[facebook]Number as sum of candidate numbers
Given a number, and a series of candidate numbers, print out all combinations, so that the sum of candidate numbers equals to the given number.
Here order is not important, so don’t print the duplicated combination.
e.g. target is 7, candidate is 2,3,6,7
output should be 7 and 3+2+2 (but not print 2+3+2, 2+2+3)