Golang给一个int数组追加一个数，数组中相邻元素的值发生变化，为什么？

Question

我正在尝试使用 Golang 解决一些动态规划问题。我写了一个像

这样的函数

func main() {
    fmt.Println(HowSum(5, []int{1, 2, 5}))
}

func HowSum(targetNum int, numbers []int) []int {
  retAry = make([][]int, targetNum+1)
  retAry[0] = make([]int, 0)
  for i := 0; i <= targetNum; i++ {
    if retAry[i] != nil {
      for _, num := range numbers {
        if i+num <= targetNum {
          fmt.Print("Before:", i, " round, num =", num, retAry, "\n")
          retAry[i+num] = append(retAry[i], num)
          fmt.Print("After :", i, " round, num =", num, retAry, "\n\n")
        }
      }
    }
  }
  return retAry[targetNum]
}

部分结果如下

...
Before:3 round, num =2 [[] [1] [1 1] [1 1 1] [1 1 1 1] [5]]
After :3 round, num =2 [[] [1] [1 1] [1 1 1] [1 1 1 2] [1 1 1 2]]
...
[1 1 1 2 1]

当程序将retAry[5]从[5]替换为[1 1 1 2]时，retAry[4]中的数组由[1 1 1 1]变为[1 1 1 2]。发生了什么？

但是，如果替换 retAry[i+num] = append(retAry[i], num) 到 retAry[i+num] = append([]int{num}, retAry[i]...) ，我可以得到正确的答案。

...
Before:3 round, num =2 [[] [1] [1 1] [1 1 1] [1 1 1 1] [5]]
After :3 round, num =2 [[] [1] [1 1] [1 1 1] [1 1 1 1] [2 1 1 1]]
...
[1 1 1 1 1]

谁能帮我解释一下我犯了什么错误？

密码是here

Answer 1

However, if replace retAry[i+num] = append(retAry[i], num) to retAry[i+num] = append([]int{num}, retAry[i]...) , I can get the correct answer.

解释：

retAry[i+num] = append(retAry[i], num) 在 retAry[i+num] 和 retAry[i] 之间共享同一个数组。如果您修改一个切片，则其他切片也可以更改。

func main() {
    s1 := append([]int{}, 1, 2, 3) // len: 3, cap 4 []int{1, 2, 3, 0}

    // it appends 4 to 4th index and assign new slice to s2.
    // s2 is share the same array with s1
    // s1 : len: 3, cap 4 []int{1, 2, 3, 4}
    // s2 : len: 4, cap 4 []int{1, 2, 3, 4}
    s2 := append(s1, 4)

    // s3 is share the same array with s1 and s2 as well
    // when you append 4th index to s1, and assign to s3, both s1 and s2 will change as well
    // s1 : len: 3, cap 4 []int{1, 2, 3, 5}
    // s2 : len: 4, cap 4 []int{1, 2, 3, 5}
    // s3 : len: 4, cap 4 []int{1, 2, 3, 5}
    s3:= append(s1, 5)
    fmt.Println(s2, s3) // output [1 2 3 5] [1 2 3 5]
}

retAry[i+num] = append([]int{num}, retAry[i]...)

[]int{num} 你用一个新数组初始化了一个新切片，然后将 retAry[i] 中的每个元素追加到新数组中。它们不再是 retAry[i+num] 和 retAry[i] 之间的任何引用。

Golang给一个int数组追加一个数，数组中相邻元素的值发生变化，为什么？

Golang append a number to an int array, the value of adjacent element in array changes, why?

arrays

append

go

解释：