Task: Largest product in a grid




Go: package main

import (
    "fmt"
    "rcu"
    "strings"
)

var grid = [][]int {
    { 8,  2, 22, 97, 38, 15,  0, 40,  0, 75,  4,  5,  7, 78, 52, 12, 50, 77, 91,  8},
    {49, 49, 99, 40, 17, 81, 18, 57, 60, 87, 17, 40, 98, 43, 69, 48,  4, 56, 62,  0},
    {81, 49, 31, 73, 55, 79, 14, 29, 93, 71, 40, 67, 53, 88, 30,  3, 49, 13, 36, 65},
    {52, 70, 95, 23,  4, 60, 11, 42, 69, 24, 68, 56,  1, 32, 56, 71, 37,  2, 36, 91},
    {22, 31, 16, 71, 51, 67, 63, 89, 41, 92, 36, 54, 22, 40, 40, 28, 66, 33, 13, 80},
    {24, 47, 32, 60, 99,  3, 45,  2, 44, 75, 33, 53, 78, 36, 84, 20, 35, 17, 12, 50},
    {32, 98, 81, 28, 64, 23, 67, 10, 26, 38, 40, 67, 59, 54, 70, 66, 18, 38, 64, 70},
    {67, 26, 20, 68,  2, 62, 12, 20, 95, 63, 94, 39, 63,  8, 40, 91, 66, 49, 94, 21},
    {24, 55, 58,  5, 66, 73, 99, 26, 97, 17, 78, 78, 96, 83, 14, 88, 34, 89, 63, 72},
    {21, 36, 23,  9, 75,  0, 76, 44, 20, 45, 35, 14,  0, 61, 33, 97, 34, 31, 33, 95},
    {78, 17, 53, 28, 22, 75, 31, 67, 15, 94,  3, 80,  4, 62, 16, 14,  9, 53, 56, 92},
    {16, 39,  5, 42, 96, 35, 31, 47, 55, 58, 88, 24,  0, 17, 54, 24, 36, 29, 85, 57},
    {86, 56,  0, 48, 35, 71, 89,  7,  5, 44, 44, 37, 44, 60, 21, 58, 51, 54, 17, 58},
    {19, 80, 81, 68,  5, 94, 47, 69, 28, 73, 92, 13, 86, 52, 17, 77,  4, 89, 55, 40},
    { 4, 52,  8, 83, 97, 35, 99, 16,  7, 97, 57, 32, 16, 26, 26, 79, 33, 27, 98, 66},
    {88, 36, 68, 87, 57, 62, 20, 72,  3, 46, 33, 67, 46, 55, 12, 32, 63, 93, 53, 69},
    { 4, 42, 16, 73, 38, 25, 39, 11, 24, 94, 72, 18,  8, 46, 29, 32, 40, 62, 76, 36},
    {20, 69, 36, 41, 72, 30, 23, 88, 34, 62, 99, 69, 82, 67, 59, 85, 74,  4, 36, 16},
    {20, 73, 35, 29, 78, 31, 90,  1, 74, 31, 49, 71, 48, 86, 81, 16, 23, 57,  5, 54},
    { 1, 70, 54, 71, 83, 51, 54, 69, 16, 92, 33, 48, 61, 43, 52,  1, 89, 19, 67, 48},
}

func main() {
    maxProd, maxR1, maxR2, maxC1, maxC2 := 0, 0, 0, 0, 0
    var maxNums [4]int
    h, w := len(grid), len(grid[0])

    
    for r := 0; r < h; r++ {
        for c := 0; c < w-4; c++ {
            prod := 1
            for i := c; i < c+4; i++ {
                prod *= grid[r][i]
            }
            if prod > maxProd {
                maxProd = prod
                for n := 0; n < 4; n++ {
                    maxNums[n] = grid[r][c+n]
                }
                maxR1, maxR2 = r, r
                maxC1, maxC2 = c, c+3
            }
        }
    }

    
    for c := 0; c < w; c++ {
        for r := 0; r < h-4; r++ {
            prod := 1
            for i := r; i < r+4; i++ {
                prod *= grid[i][c]
            }
            if prod > maxProd {
                maxProd = prod
                for n := 0; n < 4; n++ {
                    maxNums[n] = grid[r+n][c]
                }
                maxR1, maxR2 = r, r+3
                maxC1, maxC2 = c, c
            }
        }
    }

    fmt.Println("The greatest product of four adjacent numbers in the same direction (down or right) in the grid is:")
    var maxNumStrs [4]string
    for i := 0; i < 4; i++ {
        maxNumStrs[i] = fmt.Sprintf("%d", maxNums[i])
    }
    fmt.Printf("  %s = %s\n", strings.Join(maxNumStrs[:], " x "), rcu.Commatize(maxProd))
    fmt.Print("  at indices (one based): ")
    for r := maxR1; r <= maxR2; r++ {
        for c := maxC1; c <= maxC2; c++ {
            fmt.Printf("(%d, %d) ", r+1, c+1)
        }
    }
    fmt.Println()
}