# Leetcode 77. Combinations

## 題解

## DFS Back Tracking

class Solution:
    def combine(self, n: int, k: int) -> List[List[int]]:
        output = []
        def dfs(depth: int,start: int,ans: List[int]):
            if depth == k:
                output.append(ans[:])
            else:
                for i in range(start,n+1): # 每一層都要把自己排除，才不會有重複解
                    ans.append(i)
                    dfs(depth+1,i+1,ans)
                    ans.pop()
        dfs(0,1,[])
        return output