package main

import (
      "fmt"
      "strconv"
      "strings"
)

const grid20x20 = `
08 02 22 97 38 15 00 40 00 75 04 05 07 78 52 12 50 77 91 08
49 49 99 40 17 81 18 57 60 87 17 40 98 43 69 48 04 56 62 00
81 49 31 73 55 79 14 29 93 71 40 67 53 88 30 03 49 13 36 65
52 70 95 23 04 60 11 42 69 24 68 56 01 32 56 71 37 02 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 03 45 02 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 02 62 12 20 95 63 94 39 63 08 40 91 66 49 94 21
24 55 58 05 66 73 99 26 97 17 78 78 96 83 14 88 34 89 63 72
21 36 23 09 75 00 76 44 20 45 35 14 00 61 33 97 34 31 33 95
78 17 53 28 22 75 31 67 15 94 03 80 04 62 16 14 09 53 56 92
16 39 05 42 96 35 31 47 55 58 88 24 00 17 54 24 36 29 85 57
86 56 00 48 35 71 89 07 05 44 44 37 44 60 21 58 51 54 17 58
19 80 81 68 05 94 47 69 28 73 92 13 86 52 17 77 04 89 55 40
04 52 08 83 97 35 99 16 07 97 57 32 16 26 26 79 33 27 98 66
88 36 68 87 57 62 20 72 03 46 33 67 46 55 12 32 63 93 53 69
04 42 16 73 38 25 39 11 24 94 72 18 08 46 29 32 40 62 76 36
20 69 36 41 72 30 23 88 34 62 99 69 82 67 59 85 74 04 36 16
20 73 35 29 78 31 90 01 74 31 49 71 48 86 81 16 23 57 05 54
01 70 54 71 83 51 54 69 16 92 33 48 61 43 52 01 89 19 67 48
`

func parseLine(l string) []int64 {
      var dl []int64

      numbers := strings.Split(l, " ")
      for _, number := range numbers {
              n, err := strconv.ParseInt(number, 10, 0)
              if err != nil {
                      panic(err)
              }
              dl = append(dl, n)
      }
      return dl
}

func parseGrid20x20(g string) (grid [][]int64) {
      lines := strings.Split(g, "\n")
      for _, line := range lines[1 : len(lines)-1] {
              dl := parseLine(line)
              grid = append(grid, dl)
      }
      return
}

func printMaxProductInfo(m int64, i, j int, a, b, c, d int64, dir string) {
      fmt.Println(m)
      fmt.Println(i, j)
      fmt.Println("direction: ", dir)
      fmt.Println(a, b, c, d)
}

func findGreatesProduct(grid [][]int64) {
      var max int64
      var maxi, maxj int
      var direction string
      var a, b, c, d int64

      // left-right
      for i := 0; i <= 19; i++ {
              for j := 0; j <= 16; j++ {
                      prd := grid[i][j] * grid[i][j+1] * grid[i][j+2] * grid[i][j+3]
                      if prd > max {
                              max = prd
                              maxi = i
                              maxj = j
                              direction = "left-right"
                              a = grid[i][j]
                              b = grid[i][j+1]
                              c = grid[i][j+2]
                              d = grid[i][j+3]
                      }
              }
      }

      // up-down
      for i := 0; i <= 16; i++ {
              for j := 0; j <= 19; j++ {
                      prd := grid[i][j] * grid[i+1][j] * grid[i+2][j] * grid[i+3][j]
                      if prd > max {
                              max = prd
                              maxi = i
                              maxj = j
                              direction = "up-down"
                              a = grid[i][j]
                              b = grid[i+1][j]
                              c = grid[i+2][j]
                              d = grid[i+3][j]
                      }
              }
      }

      // diagonal: left*up to right*down
      for i := 0; i <= 16; i++ {
              for j := 0; j <= 16; j++ {
                      prd := grid[i][j] * grid[i+1][j+1] * grid[i+2][j+2] * grid[i+3][j+3]
                      if prd > max {
                              max = prd
                              maxi = i
                              maxj = j
                              direction = "left*up to right*down"
                              a = grid[i][j]
                              b = grid[i+1][j+1]
                              c = grid[i+2][j+2]
                              d = grid[i+3][j+3]
                      }
              }
      }

      // diagonal: right*up to left*down
      for i := 3; i <= 19; i++ {
              for j := 0; j <= 16; j++ {
                      prd := grid[i][j] * grid[i-1][j+1] * grid[i-2][j+2] * grid[i-3][j+3]
                      if prd > max {
                              max = prd
                              maxi = i
                              maxj = j
                              direction = "right*up to left*down"
                              a = grid[i][j]
                              b = grid[i-1][j+1]
                              c = grid[i-2][j+2]
                              d = grid[i-3][j+3]
                      }
              }
      }

      printMaxProductInfo(max, maxi, maxj, a, b, c, d, direction)
}

func main() {
      grid := parseGrid20x20(grid20x20)
      findGreatesProduct(grid)
}