Task: Straddling checkerboard
C++: #include <iostream>
#include <string>
#include <map>
#include <algorithm> 
using namespace std;

class StraddlingCheckerboard
{
  map<char, string> table;
  char first[10], second[10], third[10];
  int rowU, rowV;

public:
  StraddlingCheckerboard(const string &alphabet, int u, int v)
  {
    rowU = min(u, v);
    rowV = max(u, v);

    for(int i = 0, j = 0; i < 10; ++i)
    {
      if(i != u && i != v)
      {
        first[i] = alphabet[j];
        table[alphabet[j]] = '0' + i;
        ++j;
      }

      second[i] = alphabet[i+8];
      table[alphabet[i+8]] = '0' + rowU;
      table[alphabet[i+8]] += '0' + i;

      third[i] = alphabet[i+18];
      table[alphabet[i+18]] = '0' + rowV;
      table[alphabet[i+18]] += '0' + i;
    }
  }

  string encode(const string &plain)
  {
    string out;
    for(int i = 0; i < plain.size(); ++i)
    {
      char c = plain[i];
      if(c >= 'a' && c <= 'z')
        c += 'A' - 'a';

      if(c >= 'A' && c <= 'Z')
        out += table[c];
      else if(c >= '0' && c <= '9')
      {
        out += table['/'];
        out += c;
      }
    }
    return out;
  }

  string decode(const string &cipher)
  {
    string out;
    int state = 0;
    for(int i = 0; i < cipher.size(); ++i)
    {
      int n = cipher[i] - '0';
      char next = 0;

      if(state == 1)
        next = second[n];
      else if(state == 2)
        next = third[n];
      else if(state == 3)
        next = cipher[i];
      else if(n == rowU)
        state = 1;
      else if(n == rowV)
        state = 2;
      else
        next = first[n];

      if(next == '/')
        state = 3;
      else if(next != 0)
      {
        state = 0;
        out += next;
      }
    }
    return out;
  }
};

Go: package main

import (
    "fmt"
    "strings"
)

func main() {
    key := `
 8752390146
 ET AON RIS
5BC/FGHJKLM
0PQD.VWXYZU`
    p := "you have put on 7.5 pounds since I saw you."
    fmt.Println(p)
    c := enc(key, p)
    fmt.Println(c)
    fmt.Println(dec(key, c))
}

func enc(bd, pt string) (ct string) {
    enc := make(map[byte]string)
    row := strings.Split(bd, "\n")[1:]
    r2d := row[2][:1]
    r3d := row[3][:1]
    for col := 1; col <= 10; col++ {
        d := string(row[0][col])
        enc[row[1][col]] = d
        enc[row[2][col]] = r2d+d
        enc[row[3][col]] = r3d+d
    }
    num := enc['/']
    delete(enc, '/')
    delete(enc, ' ')
    for i := 0; i < len(pt); i++ {
        if c := pt[i]; c <= '9' && c >= '0' {
            ct += num + string(c)
        } else {
            if c <= 'z' && c >= 'a' {
                c -= 'a'-'A'
            }
            ct += enc[c]
        }
    }
    return
}

func dec(bd, ct string) (pt string) {
    row := strings.Split(bd, "\n")[1:]
    var cx [10]int
    for i := 1; i <= 10; i++ {
        cx[row[0][i]-'0'] = i
    }
    r2d := row[2][0]-'0'
    r3d := row[3][0]-'0'
    for i := 0; i < len(ct); i++ {
        var r int
        switch d := ct[i]-'0'; d {
        case r2d:
            r = 2
        case r3d:
            r = 3
        default:
            pt += string(row[1][cx[d]])
            continue
        }
        i++
        if b := row[r][cx[ct[i]-'0']]; b == '/' {
            i++
            pt += string(ct[i])
        } else {
            pt += string(b)
        }
    }
    return
}