Code kata. https://forum.lowyat.net/index.php?showtopic=3571866&view=findpost&p=75952192

tower.go

package main

import (
	"bufio"
	"bytes"
	"fmt"
	"io"
	"regexp"
	"strconv"
)

var debug = false

func doTower(input io.Reader) {
	re, _ := regexp.Compile("(?i)[0-9]+")

	scanner := bufio.NewScanner(input) // was os.Stdin
	scanner.Scan()

	line := scanner.Text()
	words := re.FindAllStringSubmatch(line, -1)

	width, _ := strconv.Atoi(words[0][0])
	distance, _ := strconv.Atoi(words[1][0])

	region := make([][]int, width)

	for i := 0; i < width; i++ {
		scanner.Scan()
		line := scanner.Text()
		region[i] = make([]int, width)
		words := re.FindAllStringSubmatch(line, -1)
		for k, word := range words {
			region[i][k], _ = strconv.Atoi(word[0])
		}
	}

	best := 0
	for i := 0; i < width; i++ {
		for j := 0; j < width; j++ {

			currentBest := 0

			for ii := i - distance; ii <= i+distance; ii++ {
				if ii < 0 {
					continue
				}
				if ii >= width {
					break
				}

				for jj := j - distance; jj <= j+distance; jj++ {
					if jj < 0 {
						continue
					}
					if jj >= width {
						break
					}
					currentBest += region[ii][jj]
				}
			}

			if currentBest > best {
				best = currentBest
				if debug {
					fmt.Println("best at ", i, j)
				}
			}

		}
	}

	fmt.Println(best)
}

func main() {
	input := bytes.NewBufferString(`4 1
0 1 2 0
0 0 0 0
0 0 0 0
1 0 0 0`)
	doTower(input)
	if debug {
		input := bytes.NewBufferString(`5 1
0 1 2 0 1
0 0 0 0 10
0 0 0 0 1
1 0 0 0 1
1 1 1 1 1`)
		doTower(input)
	}

}