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] ]
运用递归。 1234为例子
for i in 1234:
1 + 234(的全排列)
2 + 134（的全排列）
3 + 124（的全排列）
4 + 123 （的全排列）
对应程序的17行
1 class Solution(object): 2 def __init__(self): 3 self.res = [] 4 5 def permute(self, nums): 6 """ 7 :type nums: List[int] 8 :rtype: List[List[int]] 9 """ 10 self.help(nums, 0, len(nums)) 11 12 return self.res 13 14 def help(self, a, lo, hi): 15 if(lo == hi): 16 self.res.append(a[0:hi]) 17 for i in range(lo, hi): 18 self.swap(a, i, lo) 19 self.help(a, lo + 1, hi) 20 self.swap(a, i, lo) 21 def swap(self, a, i, j): 22 temp = a[i] 23 a[i] = a[j] 24 a[j] = temp