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All leaked interview problems are collected from Internet.

All leaked interview problems are collected from Internet.

Given two integers *n* and *k*, return all possible combinations of *k* numbers out of 1 ... *n*.

For example,

If *n* = 4 and *k* = 2, a solution is:

[ [2,4], [3,4], [2,3], [1,2], [1,3], [1,4], ]

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