输入一个array，返回这个array中元素的所有排列组合情况。

样例输入：

[1,2,3]

样例输出：

[[1, 2, 3], [1, 3, 2], [2, 1, 3], [2, 3, 1], [3, 1, 2], [3, 2, 1]]

Solution

解释部分待续

def getPermutations(array):
    permutations_rec =[]
    permutations_help(array,[],permutations_rec)
    return permutations_rec
def permutations_help(array,currentPermutaion,permutations):
    print(f"currentPermutaion{currentPermutaion}")
    if not len(array) and len(currentPermutaion):
        permutations.append(currentPermutaion)
    else:
        for i in range(len(array)):
            print(f"i = {i}")
            new_array = array[:i]+array[i+1 :]
            print(f"new_array{new_array}")
            new_permutaion = currentPermutaion+[array[i]]
            print(f"new_permutaion{new_permutaion}")
            permutations_help(new_array,new_permutaion,permutations)

print(getPermutations(array = [1,2,3]))

a = [1,2,3,4,5]
print(a[1:])
### Time: O(n*n!)
### Space: Time: O(n*n!)

output

currentPermutaion[]
i = 0
new_array[2, 3]
new_permutaion[1]
currentPermutaion[1]
i = 0
new_array[3]
new_permutaion[1, 2]
currentPermutaion[1, 2]
i = 0
new_array[]
new_permutaion[1, 2, 3]
currentPermutaion[1, 2, 3]
i = 1
new_array[2]
new_permutaion[1, 3]
currentPermutaion[1, 3]
i = 0
new_array[]
new_permutaion[1, 3, 2]
currentPermutaion[1, 3, 2]
i = 1
new_array[1, 3]
new_permutaion[2]
currentPermutaion[2]
i = 0
new_array[3]
new_permutaion[2, 1]
currentPermutaion[2, 1]
i = 0
new_array[]
new_permutaion[2, 1, 3]
currentPermutaion[2, 1, 3]
i = 1
new_array[1]
new_permutaion[2, 3]
currentPermutaion[2, 3]
i = 0
new_array[]
new_permutaion[2, 3, 1]
currentPermutaion[2, 3, 1]
i = 2
new_array[1, 2]
new_permutaion[3]
currentPermutaion[3]
i = 0
new_array[2]
new_permutaion[3, 1]
currentPermutaion[3, 1]
i = 0
new_array[]
new_permutaion[3, 1, 2]
currentPermutaion[3, 1, 2]
i = 1
new_array[1]
new_permutaion[3, 2]
currentPermutaion[3, 2]
i = 0
new_array[]
new_permutaion[3, 2, 1]
currentPermutaion[3, 2, 1]
[[1, 2, 3], [1, 3, 2], [2, 1, 3], [2, 3, 1], [3, 1, 2], [3, 2, 1]]
[2, 3, 4, 5]
[Finished in 0.6s]

Time: O(n*n!)

Space: Time: O(n*n!)