LESSON 397 OF 414 · PROJECTS: COMMAND-LINE TOOLS

CLI Tool: tr v1 — Single Char Swap in TypeScript

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:

tr(lines: string[], fromChar: string, toChar: string): string

Example:

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

Output: "bXnXnX\nXpple"

When printed:
bXnXnX
Xpple

In TypeScript, passing a string to replace only swaps the first occurrence. To replace ALL of them with a literal char, the easiest trick is line.split(fromChar).join(toChar).

The full solution:

class Solution {
    tr(lines: string[], fromChar: string, toChar: string): string {
        let result: string[] = [];
        for (let i = 0; i < lines.length; i++) {
            result.push(lines[i].split(fromChar).join(toChar));
        }
        return result.join("\n");
    }
}

STEP 1 OF 4

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CLI Tool: tr v1 — Single Char Swap in TypeScript

Tr V1 in TypeScript