77. Combinations.go

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]
    }
}