回溯算法
func combine(n int, k int) [][]int {
var res [][]int
helper(&res, []int{}, 1, n, k)
return res
}
func helper(res *[][]int, coms []int, start int, n int, k int) {
if k == 0 {
tmp := []int{}
tmp = append(tmp, coms...)
*res = append(*res, tmp)
return
}
for i := start; i <= n; i++ {
coms = append(coms, i)
helper(res, coms, i+1, n, k-1)
coms = coms[:len(coms)-1]
}
}
