【LeetCode with Python】 Combinations

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原题页面： https://oj.leetcode.com/problems/combinations/
题目类型：
难度评价：★
本文地址： http://blog.csdn.net/nerv3x3/article/details/39453269

Given two integers n and k, return all possible combinations ofk 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],
]

class Solution:

    def __init__(self):
        self.lists = [ ]

    def doCombine(self, list, n, m, k):
        if 0 == k:
            self.lists.append(list)
            return
        if m > n:
            return
        self.doCombine(list[:], n, m + 1, k)
        new_list = list
        new_list.append(m)
        self.doCombine(new_list, n, m + 1, k - 1)

    # @return a list of lists of integers
    def combine(self, n, k):
        if k > n:
            return [ ]
        self.doCombine([ ], n, 1, k)
        return self.lists