dfs的两种不同架构

第一种

def dfs(u):
    res.append(pt[:])
    if u == len(nums):
        return None

    for i in range(len(nums)):
        pt.append(nums[i])
        dfs(u + 1)
        pt.pop()


res = []
pt = []

nums = list(map(int, input().split()))
dfs(0)
print(res)

# 结果
1 2 3
[[], [1], [1, 1], [1, 1, 1], [1, 1, 2], [1, 1, 3], [1, 2], [1, 2, 1], [1, 2, 2], [1, 2, 3], [1, 3], [1, 3, 1], [1, 3, 2], [1, 3, 3], [2], [2, 1], [2, 1, 1], [2, 1, 2], [2, 1, 3], [2, 2], [2, 2, 1], [2, 2, 2], [2, 2, 3], [2, 3], [2, 3, 1], [2, 3, 2], [2, 3, 3], [3], [3, 1], [3, 1, 1], [3, 1, 2], [3, 1, 3], [3, 2], [3, 2, 1], [3, 2, 2], [3, 2, 3], [3, 3], [3, 3, 1], [3, 3, 2], [3, 3, 3]]

第二种

def dfs(u):
    res.append(pt[:])
    if u == len(nums):
        return None

    for i in range(u, len(nums)):
        pt.append(nums[i])
        dfs(i + 1)
        pt.pop()


res = [] 
pt = []

nums = list(map(int, input().split()))
dfs(0)
print(res)

# 结果
1 2 3
[[], [1], [1, 2], [1, 2, 3], [1, 3], [2], [2, 3], [3]]