package main

import (
    "fmt"
)

func diagonal(A [][]int) [][]int {
    if len(A) == 0 {
        return [][]int{}
    }

    var index int = 0

    ads := make([][]int, 2*len(A)-1, 2*len(A)-1)
    for i := 0; i < len(ads); i++ {
        ads[i] = make([]int, 0, len(A))
    }

    for column := 0; column < len(A); column++ {
        i, j := 0, column
        for j >= 0 && i < len(A) {
            ads[index] = append(ads[index], A[i][j])
            i++
            j--
        }
        index++
    }

    for row := 1; row < len(A); row++ {
        i, j := row, len(A)-1
        for j >= 0 && i < len(A) {
            ads[index] = append(ads[index], A[i][j])
            i++
            j--
        }
        index++
    }

    return ads
}

func main() {
    A := [][]int{}
    fmt.Println(diagonal(A))
}