LESSON 393 OF 410 · PROJECTS: COMMAND-LINE TOOLS

CLI Tool: tr v1 — Single Char Swap in Java

Practice

Build a tiny version of the Unix tr command. Given a list of lines and two single characters fromChar and toChar, replace every occurrence of fromChar with toChar in each line, then return the lines joined by newline characters (\n).

Notes: fromChar and toChar are single ASCII characters, taken literally (no escapes like \, no ranges). Upper and lower case are different characters. A line may be empty, and may not contain fromChar at all.

Function signature:

public String tr(List<String> lines, String fromChar, String toChar)

Example:

Input: lines = ["banana", "apple"], fromChar = "a", toChar = "X"

Output: "bXnXnX\nXpple"

When printed:
bXnXnX
Xpple

Java's String.replace(CharSequence, CharSequence) swaps EVERY occurrence (unlike replaceFirst). Apply it to each line and accumulate.

The full solution:

class Solution {
    public String tr(List<String> lines, String fromChar, String toChar) {
        List<String> result = new ArrayList<>();
        for (String line : lines) {
            result.add(line.replace(fromChar, toChar));
        }
        return String.join("\n", result);
    }
}

STEP 1 OF 4

Guided

Ctrl + Enter to check

CLI Tool: tr v1 — Single Char Swap in Java

Tr V1 in Java