3163. String Compression III

Description

Given a string word, compress it using the following algorithm:

• Begin with an empty string comp. While word is not empty, use the following operation:
  • Remove a maximum length prefix of word made of a single character c repeating at most 9 times.
  • Append the length of the prefix followed by c to comp.

Return the string comp.

 

Example 1:

Input: word = "abcde"

Output: "1a1b1c1d1e"

Explanation:

Initially, comp = "". Apply the operation 5 times, choosing "a", "b", "c", "d", and "e" as the prefix in each operation.

For each prefix, append "1" followed by the character to comp.

Example 2:

Input: word = "aaaaaaaaaaaaaabb"

Output: "9a5a2b"

Explanation:

Initially, comp = "". Apply the operation 3 times, choosing "aaaaaaaaa", "aaaaa", and "bb" as the prefix in each operation.

• For prefix "aaaaaaaaa", append "9" followed by "a" to comp.
• For prefix "aaaaa", append "5" followed by "a" to comp.
• For prefix "bb", append "2" followed by "b" to comp.

 

Constraints:

• 1 <= word.length <= 2 * 105
• word consists only of lowercase English letters.

 

Solutions

Solution: Simulation

• Time complexity: O(n)
• Space complexity: O(1)

 

JavaScript

/**
 * @param {string} word
 * @return {string}
 */
const compressedString = function (word) {
  const n = word.length;
  let repeat = 1;
  let result = '';

  for (let index = 1; index <= n; index++) {
    if (word[index] === word[index - 1] && repeat < 9) {
      repeat += 1;
      continue;
    }
    result += `${repeat}${word[index - 1]}`;
    repeat = 1;
  }
  return result;
};