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], ] 给两个数字n, k,返回所有由[1...n]中的k数字组合的可能解. 解法1: 递归 解法2: 迭代 C++: Recursion c…