〇 slice 扩容规则

〇 slice append 修改值

在解答 LeetCode 78. Subsets 时，我的原答案是

func subsets(nums []int) [][]int {
    res := make([][]int, 0)
    track := make([]int, 0)
    backtrack(track, nums, &res, 0)
    return res
}
// track 路径
// nums 选择列表
// 结束条件：start == len(nums)
func backtrack(track, nums []int, res *[][]int, start int) {
    *res = append(*res, track)
    for i := start; i < len(nums); i++ {
        track = append(track, nums[i])
        backtrack(track, nums, res, i+1)
        track = track[:len(track)-1]
    }
}

但得出的结果却是 [[] [3] [1 3] [1 2 3] [1 3] [3] [2 3] [3]]
可见某个切片的原数组的值被改动了，经过分析可知是 track 切片
由于程序运行的具体情况很复杂，在此不做分析

如果想要将一个切片的数据追加到另一个切片中，建议使用 copy 和中间变量，而非 append

package main
import "fmt"
func main() {
    s1 := [][]int{{1}, {2}, {3}}
    s2 := []int{4}
    s1 = append(s1, s2)
    fmt.Println(s1) // [[1] [2] [3] [4]]
    s2[0] *= 10
    fmt.Println(s1) // [[1] [2] [3] [40]]
}

package main
import "fmt"
func main() {
    s1 := [][]int{{1}, {2}, {3}}
    s2 := []int{4}
    temp := make([]int, len(s2))
    copy(temp, s2)
    s1 = append(s1, temp)
    fmt.Println(s1) // [[1] [2] [3] [4]]
    s2[0] *= 10
    fmt.Println(s1) // [[1] [2] [3] [4]]
}

将原答案改为

func subsets(nums []int) [][]int {
    res := make([][]int, 0)
    track := make([]int, 0)
    backtrack(track, nums, &res, 0)
    return res
}
// track 路径
// nums 选择列表
// 结束条件：start == len(nums)
func backtrack(track, nums []int, res *[][]int, start int) {
    temp := make([]int, len(track))
    copy(temp, track)
    *res = append(*res, temp)
    for i := start; i < len(nums); i++ {
        track = append(track, nums[i])
        backtrack(track, nums, res, i+1)
        track = track[:len(track)-1]
    }
}

通过题目