将新行追加到多维切片

Question

I have a function which creates a 2d slice, one row and three columns

func threeSum(nums []int) [][]int {
    result := make([][]int, 1)
    result[0] = []int{1, 2, 3}
    return result
}

What if I want to dynamically add a row?

If result was just a normal slice I would just append to the end of the slice, however with the 2d array it seems I have to manually do a lot of things, is there an easier way?

EDIT: My way of doing it would be, if I need to add a new row:

result = append(result, []int{4, 2, 3})

Which in hindsight isn't actually bad :) If anyone has an opinion I'll be happy to accept.

Answer 1

The way you present is indeed how it should be done, certainly it is the easiest way...

There is a way to do it with copy, but that would require you to manually alocate a new slice, so it would often be far slower, and in every case it would require more code.

If you need to add a new column in the middle or at the beginning of the existing ones, then you will need to alocate a new slice (or, if your current slice has unused space, increases it's length), copy the elements from the old slice to the new slice (in two operations so the slot you need for your new item is left empty), and finaly add your new item directly. This takes a minimum of 3 lines of code in the most compact case, more with bounds checking and optional higher efficency paths.