rotate_matrix.go

package main

import (
    "fmt"
)

// tl = top left
// tr = top right
// bl = bottom left
// br = bottom right

func rotateCW(m [][]byte) {
  l := len(m)
  for j := 0; j < l / 2; j++ {
    p := l - j - 1
    for i := j; i < l - j - 1; i++ {
      q := l - i - 1
      t := m[i][p]
      // tl -> tr
      m[i][p] = m[j][i]
      // bl -> tl
      m[j][i] = m[q][j]
      // br -> bl
      m[q][j] = m[p][q]
      // tr -> br
      m[p][q] = t
    }
  }
}

func rotateCCW(m [][]byte) {
  l := len(m)
  for j := 0; j < l / 2; j++ {
    p := l - j - 1
    for i := j; i < p; i++ {
      q := l - i - 1
      t := m[i][p]
      // br -> tr
      m[i][p] = m[p][q]
      // bl -> br
      m[p][q] = m[q][j]
      // tl -> tr
      m[q][j] = m[j][i]
      // tr -> tl
      m[j][i] = t
    }
  }
}

func compare(m1 [][]byte, m2 [][]byte) bool {
  if len(m1) != len(m2) {
    return false
  }
  for i := 0; i < len(m1); i++ {
    if len(m1[i]) != len(m2[i]) {
      return false
    }
    for j := 0; j < len(m1[i]); j++ {
      if m1[i][j] != m2[i][j] {
        return false
      }
    }
  }
  return true
}

func main() {
  m := [][]byte {
    { 1, 2, 3, 4, 5 },
    { 4, 5, 6, 7, 8 },
    { 7, 8, 9, 0, 1 },
    { 0, 1, 2, 3, 4 },
    { 3, 4, 5, 6, 7 },
  }

  // duplicate the matrix as a reference
  q := make([][]byte, len(m))
  for i := 0; i < len(m); i++ {
    q[i] = make([]byte, len(m))
    copy(q[i], m[i])
  }

  // rotate the matrix clockwise and counter-clockwise
  rotateCW(m)
  rotateCCW(m)

  // compare matrices
  eq := "are"
  if !compare(m, q) {
    eq += " not"
  }
  fmt.Println("The matrices", eq,  "equal")
}