// ---------------------------------------------------------
// Compress: turn "aaabbcccc" into "a3b2c4"
// This is run-length encoding (RLE)
// ---------------------------------------------------------
function compress(s) {
if (!s) {
return ""; // Edge case: empty string
}
let out = []; // Result string (array for efficiency)
let count = 1; // Count of repeated characters
// Start from index 1 and compare with previous character
for (let i = 1; i <= s.length; i++) {
// If still repeating the same character, increase count
if (i < s.length && s[i] === s[i - 1]) {
count++;
} else {
// Character changed OR reached end of string
out.push(s[i - 1]); // Add the character
out.push(String(count)); // Add how many times it repeated
count = 1; // Reset counter
}
}
return out.join("");
}
// ---------------------------------------------------------
// Decompress: turn "a3b2c4" into "aaabbcccc"
// Reads a letter, then reads digits, expands them.
// ---------------------------------------------------------
function decompress(s) {
let out = []; // Result string
let currentChar = null; // The character being processed
let number = []; // Digits representing the count
for (const c of s) {
if (/[A-Za-z]/.test(c)) { // Found a letter
// If we already have a previous letter + number, expand it
if (currentChar !== null && number.length > 0) {
const count = Number(number.join(""));
out.push(currentChar.repeat(count));
}
currentChar = c; // Start new character
number = []; // Reset number buffer
} else if (/\d/.test(c)) { // Found a digit
number.push(c); // Build multi-digit number
}
}
// Handle the last character + number pair
if (currentChar !== null && number.length > 0) {
const count = Number(number.join(""));
out.push(currentChar.repeat(count));
}
return out.join("");
}
function main() {
const s = "wwwwwwwwwwwwbwwwwwwwwwwbbbwwwwwwccccwwwwwwwwwwww";
const c = compress(s);
const d = decompress(c);
console.log("Original: ", s);
console.log("Compressed: ", c);
console.log("Decompressed:", d);
}
main();
/*
run:
Original: wwwwwwwwwwwwbwwwwwwwwwwbbbwwwwwwccccwwwwwwwwwwww
Compressed: w12b1w10b3w6c4w12
Decompressed: wwwwwwwwwwwwbwwwwwwwwwwbbbwwwwwwccccwwwwwwwwwwww
*/
