Zipstring

What is zipstring

zipstring is a function that takes a string and returns a new string that replaces every character with the number of duplicates and the character itself, deleting the extra duplications.

Zipstring step by step

First step

First since we got to print the numbers of duplicates at the beggining of the word instead of the end, we are going to loop over our given string backwards.
That way we can count while we iterate throught the string and print a number when we encounter something different.

for i := len(s) - 1; i >= 0; i-- {
}

Second step

Then, we will need to add a count variable that will be incremented everytime we encounter the same letter as before.

count := 0
for i := len(s) - 1; i >= 0; i-- {
  if s[i] == s[i-1] {
            count++
        }
}    

Third step

When the letter is different, we need to add to a result variable the letter plus the number of times it appeared and reset the count to 1 (minimum value).

result := ""
else if s[i] != s[i-1] {
    result = strconv.Itoa(count) + string(s[i]) + result
    count = 1
}

Keep in mind that we will need to use Itoa function on the count as it is a int and we want to work with strings.
We also need to convert s[i] to a string since that's a byte when iterating over the string.
Function should now looks like this:

result := ""
count := 1
for i := len(s) - 1; i >= 0; i-- {
  if s[i] == s[i-1] {
        count++
    } else if s[i] != s[i-1] {
        result = strconv.Itoa(count) + string(s[i]) + result
        count = 1
    }
}

Fourth and final step

We then add a final condition that will be applied first for the last iteration, when i is equal to 0.

if i == 0 {
    result = strconv.Itoa(count) + string(s[i]) + result
}

Full code

package main

import (
    "fmt"
    "strconv"
)

func zipstring(s string) string {
    result := ""
    count := 1
  //first step
    for i := len(s) - 1; i >= 0; i-- {
    //final step
        if i == 0 {
            result = strconv.Itoa(count) + string(s[i]) + result
      //second step
        } else if s[i] == s[i-1] {
            count++
      //third step
        } else if s[i] != s[i-1] {
            result = strconv.Itoa(count) + string(s[i]) + result
            count = 1
        }
    }
    return result
}