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LESSON 384 OF 414 · PROJECTS: COMMAND-LINE TOOLS

CLI Tool: wc v4 — Mode Flag in TypeScript

Practice

Combine the previous three versions of wc. Given a list of lines and a mode flag, return the requested count(s) as a string. This is our own simplified interface, not the real wc flags: the real tool combines flags (such as -lw) and pads its columns with spaces.

Function signature:

wc(lines: string[], mode: string): string

Mode values:

  • "l" → line count, as a string.
  • "w" → word count (whitespace-separated tokens), as a string.
  • "c" → character count (lines only, no separating newlines), as a string.
  • "all" → lines + "\t" + words + "\t" + chars.

The "c" count is the one from v3 (the sum of the line lengths, no newlines). Any other mode value, for example "x" or "L" (modes are case-sensitive), gives the same result as "all". For an empty list, "l", "w" and "c" give "0" and "all" gives "0<TAB>0<TAB>0". The input is plain ASCII text.

Example:

Input: lines = ["hello", "world"], mode = "all"

Output: "2\t2\t10"

2 lines, 2 words (one per line), 10 characters total.


Compute all three counts in a single pass through lines, then branch on mode to pick the return value.

let numLines: number = lines.length;
let numWords: number = 0;
let numChars: number = 0;
for (const line of lines) {
    numWords += line.trim().split(/\s+/).filter(x => x).length;
    numChars += line.length;
}
Then String(numLines) / String(numWords) / String(numChars) as needed, or assemble all three with tabs.

The full solution:
class Solution {
    wc(lines: string[], mode: string): string {
        let numLines: number = lines.length;
        let numWords: number = 0;
        let numChars: number = 0;
        for (const line of lines) {
            numWords += line.trim().split(/\s+/).filter(x => x).length;
            numChars += line.length;
        }
        if (mode === "l") { return String(numLines); }
        if (mode === "w") { return String(numWords); }
        if (mode === "c") { return String(numChars); }
        return numLines + "\t" + numWords + "\t" + numChars;
    }
}

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    Wc V4 in TypeScript

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