Value has been changed in method - go

Question

I'm solving a problem in leetcode using recursion.
But, the value which is used as a parameter is changed in the method.
package main
import "fmt"
func makeCmbs(cmbs [][]int, nums []int, remains []int, k int) [][]int {
fmt.Println("==", cmbs, nums, remains, k) // (2)
if k == 0 {
cmbs = append(cmbs, nums)
fmt.Println("!", nums, cmbs)
return cmbs
}
for i, num := range remains {
fmt.Printf("-[%d] num:%d cmbs:%v remains:%v\n", i, num, cmbs, remains) // (1) cmbs here is [[1,2,3,4]]
cmbs = makeCmbs(cmbs, append(nums, num), remains[i+1:], k-1) // cmbs in makeCmbs method is [[1,2,3,5]] ???
fmt.Printf("+[%d] num:%d cmbs:%v\n", i, num, cmbs)
}
return cmbs
}
func combine(n int, k int) [][]int {
remains := make([]int, n)
for i := 0; i < n; i++ {
remains[i] = i + 1
}
return makeCmbs([][]int{}, []int{}, remains, k)
}
func main() {
combine(5, 4)
}
Bellow is its beginning of output.
== [] [] [1 2 3 4 5] 4
-[0] num:1 cmbs:[] remains:[1 2 3 4 5]
== [] [1] [2 3 4 5] 3
-[0] num:2 cmbs:[] remains:[2 3 4 5]
== [] [1 2] [3 4 5] 2
-[0] num:3 cmbs:[] remains:[3 4 5]
== [] [1 2 3] [4 5] 1
-[0] num:4 cmbs:[] remains:[4 5]
== [] [1 2 3 4] [5] 0
! [1 2 3 4] [[1 2 3 4]]
+[0] num:4 cmbs:[[1 2 3 4]]
-[1] num:5 cmbs:[[1 2 3 4]] remains:[4 5] <---- cmbs is [[1 2 3 4]]
== [[1 2 3 5]] [1 2 3 5] [] 0 <---- why [[1 2 3 5]] ???
As you can see those last two lines, cmbs [[1 2 3 4]] became [[1 2 3 5]].
Could anybody please give me a clue why cmbs value is changed in makeCmbs method?

Answer 1

Let start with recursion last recursive loop of calling makeCmbs
cmbs = makeCmbs(cmbs, append(nums, num), remains[i+1:], k-1)
As remains[i+1:] where the value of i at last loop will be the highest i.e
i = len(remains-1)
So it means it means i+1 is two (2) greater then len(remains-1) that is why remain[i+1] will be empty array ([]) for first two last recusrive rounds.
This is how it works. I hope I made it to the imaginative height of this problem.
UPDATE:
For the first time when k=0
start of function: num:[1 2 3 4] cmbs:[] remains:[5], k:0
So if k=0 condition is true
if k == 0 {
cmbs = append(cmbs, nums)
fmt.Printf("in side if: num:%d cmbs:%v k:%v\n", nums, cmbs, k)
return cmbs
}
that is the first return of recursion
as cmbs = [] and nums = [1 2 3 4]
cmbs = append(cmbs, nums)
Now retuned value is cmb from if condition is [[1 2 3 4]] to the for loop this line
cmbs = makeCmbs(cmbs, append(nums, num), remains[i+1:], k-1)
and here loop ends so it also return the same
[[1 2 3 4]]
But at before that recursion nums was append of nums+num that is [1 2 3 5] so that is why when it return back in the second last recursion at the same for loop call cmbs hold [1 2 3 5].
It is indeed a difficult question to image but can be solved easily with a debugger.