LESSON 381 OF 404 · PROJECTS: COMMAND-LINE TOOLS

CLI Tool: uniq v3 — Duplicates Only in Go

Practice

Build a version of the Unix uniq -d command. Given a list of lines, output only the values whose adjacent run length is greater than one — i.e. lines that actually repeat back-to-back. Each surviving value is printed once (no count, just the value), joined by \n.

Function signature:

func uniqDups(lines []string) string

Example:

Input: lines = ["a", "a", "b", "c", "c", "c"]

Output: "a\nc"

When printed:
a
c

The run of "a"s has length 2 and the run of "c"s has length 3, so both survive. The single "b" is dropped.

Track prev and count. When the line changes (or after the loop), flush prev only if count > 1. After collecting the survivors, join them with "\n" using strings.Join.

if count > 1 {
    result = append(result, prev)
}

The full solution:

func uniqDups(lines []string) string {
    result := []string{}
    count := 0
    prev := ""
    for i := 0; i < len(lines); i++ {
        if count > 0 && lines[i] == prev {
            count++
        } else {
            if count > 1 {
                result = append(result, prev)
            }
            prev = lines[i]
            count = 1
        }
    }
    if count > 1 {
        result = append(result, prev)
    }
    return strings.Join(result, "\n")
}

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CLI Tool: uniq v3 — Duplicates Only in Go

Uniq V3 in Go