Go Coding with Asparagos: Tomato Discrimination in the Soup Queue

Hi! I'm Asparagos — an asparagus who codes in Go. Here you’ll find everyday problems that a typical veggie might struggle with — and my Go solutions to them. Today we are solving the problem of Tomato discrimination 🍅.

Tomatoes are now fruits. Can the soup survive?

Problem

Vegetables are waiting in a queue to be added to the soup.
Suddenly, the Botanical Government passes a new law: tomatoes are now officially fruits!

Thankfully, everybody still loves tomatoes in soups, so they won’t be removed.
But there’s a catch: all tomatoes must now be moved to the end of the queue, no matter where they were before the law. The order of all other vegetables must remain unchanged.

Be careful: some of them will try to mislead you by calling themselves pomodoro.
Don’t fall for it — anyone who calls themselves "tomato" or "pomodoro" must go to the end.
Also, to avoid further confusion, rename all "pomodoro" to "tomato" before adding them to the end.

Input 🥦

A slice of strings — each string represents a vegetable.
Only lowercase letters are allowed.
Only "tomato" and "pomodoro" should be discriminated.

Output 🥕

A slice of strings — each string represents a vegetable.
The order of all non-tomatoes stays the same.
All "tomato" and "pomodoro" (renamed to "tomato") appear at the end of the queue.

Examples 🥒:

• Example 1

  Input: ["cucumber", "tomato", "pepper", "tomato", "lettuce"]

  Output: ["cucumber", "pepper", "lettuce", "tomato", "tomato"]

• Example 2

  Input: ["tomato", "pomodoro", "lettuce"]

  Output: ["lettuce", "tomato", "tomato"]

• Example 3

  Input: ["cucumber", "pepper", "lettuce"]

  Output: ["cucumber", "pepper", "lettuce"]

• Example 4

  Input: []

  Output: []

Solution 💡

1. First, we define a helper function that checks whether a vegetable is "tomato" or "pomodoro".

2. The main function modifies the input slice in-place.
   We use a writeInd pointer to track the position where the next non-tomato vegetable should be written.
   We iterate through the slice:

   If the current element is a tomato (or pomodoro), we skip it.

   If it's a non-tomato vegetable, we copy it to vegetables[writeInd] and increment writeInd.

   After this loop, all non-tomato vegetables are in their correct positions, in the original order.

3. Next, we fill the remaining part of the slice (starting from writeInd) with "tomato" — because all "pomodoro" should be renamed to "tomato".
   

func isTomato(vegetable string) bool {
    return vegetable == "tomato" || vegetable == "pomodoro"
}

// discriminateTomatoes reorders the slice in-place.
func discriminateTomatoes(vegetables []string) {
    writeInd := 0
    for _, vegetable := range vegetables {
        if !isTomato(vegetable) {
            vegetables[writeInd] = vegetable
            writeInd++
        }
    }
    for writeInd < len(vegetables) {
        vegetables[writeInd] = "tomato"
        writeInd++
    }
}

Feel free to check out the full code with tests on GitHub, and don’t hesitate to leave a ⭐ if you find it helpful!