LESSON 385 OF 410 · PROJECTS: COMMAND-LINE TOOLS

CLI Tool: uniq v1 — Drop Adjacent Duplicates in Java

Practice

Build a tiny version of the Unix uniq command. Given a list of lines, drop adjacent duplicate lines (keep only the first occurrence in each consecutive run) and return the surviving lines joined by newline characters (\n).

Function signature:

public String uniq(List<String> lines)

Example:

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

Output: "a\nb\nc\na"

When printed:
a
b
c
a

Notice that the trailing "a" survives because it is not adjacent to the first run of "a"s — only consecutive duplicates are removed.

Build a List<String> result and add the current line only if it differs from the last entry in result. Use .equals() for the comparison, NOT ==.

if (result.isEmpty() || !lines.get(i).equals(result.get(result.size() - 1))) {
    result.add(lines.get(i));
}

The full solution:

class Solution {
    public String uniq(List<String> lines) {
        List<String> result = new ArrayList<>();
        for (int i = 0; i < lines.size(); i++) {
            if (result.isEmpty() || !lines.get(i).equals(result.get(result.size() - 1))) {
                result.add(lines.get(i));
            }
        }
        return String.join("\n", result);
    }
}

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CLI Tool: uniq v1 — Drop Adjacent Duplicates in Java

Uniq V1 in Java