77. 组合 @Python @Go

原题

https://leetcode.cn/problems/combinations/description/

思路

回溯法

复杂度

时间：O(C(n, k))
空间：O(C(n, k))

Python代码

class Solution:
    def combine(self, n: int, k: int) -> List[List[int]]:
        ans = []

        def dfs(start, path):
            # 返回条件
            if len(path) == k:
                ans.append(path[:])
                return 

            for i in range(start, n+1):
                path.append(i)
                dfs(i + 1, path)
                # 还原
                path.pop()
            
        dfs(1, [])
        return ans         

        

Go代码

func combine(n int, k int) [][]int {
	var ans [][]int
	var dfs func(int, []int)
	dfs = func(start int, path []int) {
		// 返回条件
		if len(path) == k {
			// 复制路径
			com := make([]int, len(path))
			copy(com, path)
			ans = append(ans, com)
			return
		}
		for i := start; i <= n; i++ {
			path = append(path, i)
			dfs(i+1, path)
			// 还原
			path = path[:len(path)-1]
		}
	}
	dfs(1, []int{})
	return ans
}