回溯-排列型

 利用哈希表

class Solution:
    def permute(self, nums: List[int]) -> List[List[int]]:
        ans = []
        path = []
        n = len(nums)

        def dfs(i, s):
            if i==n:
                ans.append(path[:])
                return
            
            for x in s:
                path.append(x)
                dfs(i+1, s-{x})
                path.pop()
            
        dfs(0, set(nums))
        return ans

利用访问数组

class Solution:
    def permute(self, nums: List[int]) -> List[List[int]]:
        ans = []
        path = []
        n = len(nums)
        on_path = [False]*n

        def dfs(i):
            if i==n:
                ans.append(path[:])
                return
            
            for j in range(n):
                if not on_path[j]:
                    path.append(nums[j])
                    on_path[j] = True
                    dfs(i+1)
                    on_path[j] = False
                    path.pop()
            
        dfs(0)
        return ans

直接将nums[i] 的元素超出题目设置范围

class Solution:
    def permute(self, nums: List[int]) -> List[List[int]]:
        ans = []
        path = []
        n = len(nums)

        def dfs(i):
            if i==n:
                ans.append(path[:])
                return
            
            for j in range(n):
                if nums[j] <=10 :
                    path.append(nums[j])
                    nums[j]+=100
                    dfs(i+1)
                    nums[j]-=100
                    path.pop()
            
        dfs(0)
        return ans