KeepOnlyKConsecutiveLetters.java

package com.rampatra.strings;

/**
 * @author rampatra
 * @since 30/11/2018
 */
public class KeepOnlyKConsecutiveLetters {

    /**
     * A method which takes a string {@code str} and a number {@code k} and
     * returns a string with at most {@code k} consecutive characters in the
     * string.
     * <p>
     * For example,
     * 1) aaaaaabbbbbccccc, 3 -> aaabbbccc
     * 2) abc, 2 -> abc
     * 3) aabbccc, 3 -> aabbccc
     *
     * @param str input string
     * @param k
     * @return a string with at most {@code k} consecutive characters
     */
    private static String keepOnlyKConsecutiveLetters(String str, int k) {
        StringBuilder sb = new StringBuilder();
        int count = 0;

        for (int i = 0; i < str.length(); i++) {
            if (i != 0 && str.charAt(i) != str.charAt(i - 1)) {
                count = 0;
            }
            if (count < k) {
                sb.append(str.charAt(i));
                count++;
            }
        }

        return sb.toString();
    }

    public static void main(String[] args) {
        System.out.println("aaaaabbbbbccccc, 5: " + keepOnlyKConsecutiveLetters("aaaaabbbbbccccc", 5));
        System.out.println("aaaaabbbbbccccc, 2: " + keepOnlyKConsecutiveLetters("aaaaabbbbbccccc", 2));
        System.out.println("aaaaabbbbbccccc, 1: " + keepOnlyKConsecutiveLetters("aaaaabbbbbccccc", 1));
        System.out.println("aabbcc, 2: " + keepOnlyKConsecutiveLetters("aabbcc", 2));
        System.out.println("aabbcc, 0: " + keepOnlyKConsecutiveLetters("aabbcc", 0));
        System.out.println("abc, 2: " + keepOnlyKConsecutiveLetters("abc", 2));
    }
}