排列组合问题

一.不同元素子集问题

78. Subsets

Given a set of distinct integers, nums, return all possible subsets. 
给定一组非重复数字，求出所有可能的子集

解析：

例如 [1,2,3]，解法： 
首先放[]，然后往已有的[]中放1 
1. 首先放1 
此时已有[ [], 1 ] 
2. 然后对[ [], 1 ] 放2 
于是此时有 [ [], [1], [2], [1,2] ] 
3. 然后对[ [], [1], [2], [1,2] ] 放3 
此时[ [], [1], [2], [1,2], [3], [1,3], [2,3], [1,2,3] ] 求出解

#encoding:utf-8
_author_ = "Wang Wenchao"
def fun(ls):
    result=[]
    st=[]
    result.append(st)
    for i in ls:
        for j in range(len(result)):
            x=result[j][:] #复制列表
            x.append(i)
            result.append(x)
    return result
ls=[1,2,3]
print fun(ls)

　　运行结果    [[], [1], [2], [1, 2], [3], [1, 3], [2, 3], [1, 2, 3]]

二.全排列组合

46.Permutations(排列组合)

Permutations

Given a collection of 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], and [3,2,1].