443. String Compression

Problem Statement Source

Poor description but it is what it is.

Given an array of characters chars, compress it using the following algorithm: Begin with an empty string s. For each group of consecutive repeating characters in chars:

• If the group’s length is 1, append the character to s.
• Otherwise, append the character followed by the group’s length.

The compressed string s should not be returned separately, but instead, be stored in the input character array chars. Note that group lengths that are 10 or longer will be split into multiple characters in chars. After you are done modifying the input array, return the new length of the array. You must write an algorithm that uses only constant extra space.

Example 1:

Input: chars = [“a”,“a”,“b”,“b”,“c”,“c”,“c”] Output: Return 6, and the first 6 characters of the input array should be: [“a”,“2”,“b”,“2”,“c”,“3”] Explanation: The groups are “aa”, “bb”, and “ccc”. This compresses to “a2b2c3”.

Example 2:

Input: chars = [“a”] Output: Return 1, and the first character of the input array should be: [“a”] Explanation: The only group is “a”, which remains uncompressed since it’s a single character.

Example 3:

Input: chars = [“a”,“b”,“b”,“b”,“b”,“b”,“b”,“b”,“b”,“b”,“b”,“b”,“b”] Output: Return 4, and the first 4 characters of the input array should be: [“a”,“b”,“1”,“2”]. Explanation: The groups are “a” and “bbbbbbbbbbbb”. This compresses to “ab12”.

Constraints:

• 1 <= chars.length <= 2000
• chars[i] is a lowercase English letter, uppercase English letter, digit, or symbol.

Solution - Pepcoding

Algorithm:

class Solution {
    public int compress(char[] chars) {
 
        StringBuilder sb = new StringBuilder();
 
        int index = 1;
        int count = 1;
		sb.append(chars[0]);
		
        while(index < chars.length){
            if(chars[index] != chars[index-1]){
	            if(count > 1){
                    sb.append(count);
                }
                sb.append(chars[index]);
                count = 1; //reset the counter for new char
            } else{
                count++;
            }
            index++;
        }
 
        if(count > 1){
            sb.append(count);
        }
 
        /*
        modify the chars array inplace using StringBuilder's result
        Because we're returning the length of the modified char array, I think woh utna hi modifiedlength le lega solution, that's why it got
        submitted and won't consider the left out elements in the array.
        */
        for(int i = 0; i < sb.length(); i++){
            chars[i] = sb.charAt(i);
        }
        return sb.length();
    }
}