最近刷了一波排列组合以及子集问题 主要学会理解for循环中 i 与 pos 以及level的这些变量的理解
这个可以从递归树来判别
#题目:排列
Given a collection of distinct numbers, return all possible permutations.
For example,
[1,2,3] have the following permutations:
[
[1,2,3],
[1,3,2],
[2,1,3],
[2,3,1],
[3,1,2],
[3,2,1]
]
并不用考虑重复
主要是看 递归树图
上代码:
#题目:子集
Given a set of distinct integers, nums, return all possible subsets.
Note: The solution set must not contain duplicate subsets.
For example,
If nums = [1,2,3], a solution is:
[
[3],
[1],
[2],
[1,2,3],
[1,3],
[2,3],
[1,2],
[]
]
并不用考虑重复
上代码:
#题目:组合
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],
]
并不用考虑重复
上代码: