为什么我的范围在切片中显示不存在的值

Question

我试图在Go中解决Leetcode问题。问题在于子集。

这是我用一些调试日志写的全部代码：

package main
import (
"fmt"
)
func main() {
v := []int{9, 0, 3, 5, 7}
fmt.Println(subsets(v))
}
func subsets(nums []int) [][]int {
result := [][]int{
[]int{}, // empty
}
for _, num := range nums {  
fmt.Println("==========")
fmt.Println(num)
fmt.Printf("result = %vn", result)
temp := [][]int{}
for _, r := range result {
fmt.Printf("r = %vn", r)
temp = append(temp, append(r, num))
}
for _, t := range temp {
result = append(result, t)
}
fmt.Println("==========")       
}
return result
}

(我还准备了Go play ground URL(

这是上面代码的输出：

==========
9
result = [[]]
r = []
==========
==========
0
result = [[] [9]]
r = []
r = [9]
==========
==========
3
result = [[] [9] [0] [9 0]]
r = []
r = [9]
r = [0]
r = [9 0]
==========
==========
5
result = [[] [9] [0] [9 0] [3] [9 3] [0 3] [9 0 3]]
r = []
r = [9]
r = [0]
r = [9 0]
r = [3]
r = [9 3]
r = [0 3]
r = [9 0 3]
==========
==========
7
result = [[] [9] [0] [9 0] [3] [9 3] [0 3] [9 0 3] [5] [9 5] [0 5] [9 0 5] [3 5] [9 3 5] [0 3 5] [9 0 3 5]] // (a)
r = []
r = [9]
r = [0]
r = [9 0]
r = [3]
r = [9 3]
r = [0 3]
r = [9 0 3]
r = [5]
r = [9 5]
r = [0 5]
r = [9 0 5]
r = [3 5]
r = [9 3 5]
r = [0 3 5]
r = [9 0 3 7] // (b)
==========
[[] [9] [0] [9 0] [3] [9 3] [0 3] [9 0 3] [5] [9 5] [0 5] [9 0 5] [3 5] [9 3 5] [0 3 5] [9 0 3 7] [7] [9 7] [0 7] [9 0 7] [3 7] [9 3 7] [0 3 7] [9 0 3 7] [5 7] [9 5 7] [0 5 7] [9 0 5 7] [3 5 7] [9 3 5 7] [0 3 5 7] [9 0 3 7 7]]

让我们看第5个result。(我指出那里是(a)(从那里开始，result的最后一个元素是[9, 0, 3, 5]，这是预期的行为。然而，在那之后，当我试图在result中编写元素的调试日志时，它会更改为[9, 0, 3, 7]((b)(。

你知道为什么吗？

Answer 1

append在需要时更改r：
而不是：

temp = append(temp, append(r, num))

您可以使用：

rr := make([]int, len(r))
copy(rr, r)
rr = append(rr, num)
temp = append(temp, rr)

你可以去：

package main
import (
"fmt"
)
func main() {
v := []int{9, 0, 3, 5, 7}
fmt.Println(subsets(v))
}
func subsets(nums []int) [][]int {
result := [][]int{
[]int{}, // empty
}
for _, num := range nums {
fmt.Println("==========")
fmt.Println(num)
fmt.Printf("result = %vn", result)
temp := [][]int{}
for _, r := range result {
fmt.Printf("r = %vn", r)
// append(r, num)
rr := make([]int, len(r))
copy(rr, r)
rr = append(rr, num)
temp = append(temp, rr)
}
for _, t := range temp {
result = append(result, t)
}
fmt.Println("==========")
}
return result
}

只要调试你的代码，你就会看到，它发生在这里：

temp := [][]int{}
for _, r := range result {
fmt.Println("result =", result, len(result), cap(result))
fmt.Println("r ==", r, len(r), cap(r))
fmt.Println("num =", num)
rr := append(r, num)
fmt.Println("r ==", r, len(r), cap(r))
fmt.Println("rr ==", rr, len(rr), cap(rr))
fmt.Println("result =", result, len(result), cap(result))
fmt.Println("temp =", temp)
temp = append(temp, rr)
fmt.Println("temp =", temp)
}

当

result = [[] [9] [0] [9 0] [3] [9 3] [0 3] [9 0 3] [5] [9 5] [0 5] [9 0 5] [3 5] [9 3 5] [0 3 5] [9 0 3 5]] 16 16
r == [9 0 3] 3 4
num = 7
r == [9 0 3] 3 4
rr == [9 0 3 7] 4 4
result = [[] [9] [0] [9 0] [3] [9 3] [0 3] [9 0 3] [5] [9 5] [0 5] [9 0 5] [3 5] [9 3 5] [0 3 5] [9 0 3 7]] 16 16

原因：

append(r, num)