LESSON 386 OF 410 · PROJECTS: COMMAND-LINE TOOLS

CLI Tool: uniq v2 — Count Adjacent Runs in Java

Practice

Build a version of the Unix uniq -c command. Given a list of lines, collapse each run of adjacent duplicates into a single output line that shows the run's count followed by the value.

Each output line is formatted as String.format("%7d %s", count, value): a 7-character right-aligned count, a single space, then the line value. Join all output lines with \n.

Function signature:

public String uniqCount(List<String> lines)

Example:

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

Output (when printed):
      2 a
      1 b
      3 c

The first run is two "a"s, then a single "b", then three "c"s — three output lines.

Track String prev and int count. When a NEW value comes in (or you reach end), flush the previous run with String.format("%7d %s", count, prev) and reset.

Don't forget to flush AFTER the loop too. Use .equals() for the string comparison.

if (count > 0 && lines.get(i).equals(prev)) {
    count++;
} else {
    if (count > 0) {
        result.add(String.format("%7d %s", count, prev));
    }
    prev = lines.get(i);
    count = 1;
}

The full solution:

class Solution {
    public String uniqCount(List<String> lines) {
        List<String> result = new ArrayList<>();
        int count = 0;
        String prev = null;
        for (int i = 0; i < lines.size(); i++) {
            if (count > 0 && lines.get(i).equals(prev)) {
                count++;
            } else {
                if (count > 0) {
                    result.add(String.format("%7d %s", count, prev));
                }
                prev = lines.get(i);
                count = 1;
            }
        }
        if (count > 0) {
            result.add(String.format("%7d %s", count, prev));
        }
        return String.join("\n", result);
    }
}

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CLI Tool: uniq v2 — Count Adjacent Runs in Java

Uniq V2 in Java