Slice's pit

1. When the Slice capacity is not enough, append will become a newly generated slice.

See the "pit" of filling in the append of golang slice - Zhihu (zhihu.com)

2. The result remains unchanged when appending

In question 46 of leetcode, my code is as follows

func permute(nums []int) [][]int {
    if len(nums) == 0{
        return [][]int{}
    }
    result := [][]int{}
    track := []int{}
    used := make([]bool, len(nums))
    backtrack(nums, &track, &used, &result)
    return result
}

func backtrack(nums []int, track *[]int, used *[]bool, result *[][]int){
    // 触发结束条件
    if len(*track) == len(nums){
        temp := make([]int, len(*track))
		copy(temp, *track) // 一定要copy到temp中再append，不能直接把*track append到*result中
        *result = append(*result, temp)
        return
    }

    for idx, num := range nums{
        // 排除不合法的选择
        if (*used)[idx]{
            continue // nums[idx]已经做过选择
        }
        // 做选择
        *track = append(*track, num)
        (*used)[idx] = true
        // 进入下一层决策树
        backtrack(nums, track, used, result)
        // 撤销选择
        *track = (*track)[:len(*track)-1]
        (*used)[idx] = false
    }
    return
}

 In this code

 My original intention is to append *track to *result, but the result of appending directly is wrong and the result remains unchanged. However, if I copy it and then append to *result, it will be correct, so it is obviously not the capacity of the first slice. At present, I haven’t found the reason yet, it’s already late at night, I’ll fill in the holes later when I find the reason.