LESSON 392 OF 415 · PROJECTS: COMMAND-LINE TOOLS

CLI Tool: uniq v3 — Duplicates Only in Swift

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. Compare strings with ==.

if count > 1 {
    result.append(prev)
}

The full solution:

class Solution {
    func uniqDups(_ lines: [String]) -> String {
        var result = [String]()
        var count = 0
        var prev = ""
        for i in 0..<lines.count {
            if count > 0 && lines[i] == prev {
                count += 1
            } else {
                if count > 1 {
                    result.append(prev)
                }
                prev = lines[i]
                count = 1
            }
        }
        if count > 1 {
            result.append(prev)
        }
        return result.joined(separator: "\n")
    }
}

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CLI Tool: uniq v3 — Duplicates Only in Swift

Uniq V3 in Swift