A Tour of Go: Exercise: Slices

package main

import (
    "fmt"
    "golang.org/x/tour/pic"
)

// Used in func duplicate
var P = Pascal(11)

// The x, y of the pic
const SIZE = 256

// Add a 0 at the beginning(right shift) or at the end (left shift)
func Shift(x []uint8, left_or_right int) []uint8 {
    if left_or_right == -1 {
        return append(x, 0)
    }

    L := []uint8{0}
    n := len(x)

    for i := 0; i < n; i++ {
        L = append(L, x[i])
    }

    return L
}

// Add the two shifts to form pascal triangle
/*
                1
(1)         1       1
(2)     1       2       1
    1       3       3       1
............................. so on ...
[1 0] +
[0 1] =
[1 1] (1) --> Shift --> [1 1 0] +
                        [0 1 1]
                        [1 2 1] (2)
............................. so on ...
*/
func Add(x, y []uint8) []uint8 {
    L := make([]uint8, len(x))

    for i := range L {
        L[i] = x[i] + y[i]
    }

    return L
}

func Pascal(x int) []uint8 {
    if x == 1 {
        return []uint8{1}
    }

    L := make([]uint8, x)
    L = Pascal(x - 1)

    return Add(Shift(L, -1), Shift(L, 1))
}

// Take the P = Pascal(11) and copy it on each
// row as many times as it can be copied
func duplicate(x []uint8, d int) []uint8 {
    if d < 11 {
        for i := SIZE - d; i < SIZE; i++ {
            x[i] = P[(i+d)-SIZE]
        }
        return x
    }

    for i := SIZE - d; i < SIZE-d+11; i++ {
        x[i] = P[(i+d)-SIZE]
    }

    return duplicate(x, d-11)
}

func Pic(dx, dy int) [][]uint8 {
    rows := make([][]uint8, dy)

    // Init of each row
    for i := range rows {
        rows[i] = make([]uint8, dx)
    }

    // Fill the rows
    for i := range rows {
        rows[i] = duplicate(rows[i], cap(rows[i]))
    }

    return rows

}

func main() {
    pic.Show(Pic)
}