LESSON 625 OF 678 · PROJECTS: COMMAND-LINE TOOLS

CLI Tool: uniq v4 — Loners Only

Practice

Build a version of the Unix uniq -u command. Given a list of lines, output only the values whose adjacent run length is exactly one — i.e. lines that did NOT repeat back-to-back. Surviving values are joined by \n.

Function signature:

func uniqOnce(_ lines: [String]) -> String

Example:

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

Output: "b"

When printed:
b

The two "a"s and the three "c"s are dropped because their runs are longer than 1. Only the lone "b" survives.

Track prev and count. When the line changes (or after the loop), flush prev only if count == 1.

if count == 1 {
    result.append(prev!)
}

In Swift, == compares string values directly.

The full solution:

class Solution {
    func uniqOnce(_ lines: [String]) -> String {
        var result = [String]()
        var count = 0
        var prev: String? = nil
        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")
    }
}

STEP 1 OF 13

Guided

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