_1370.java

package com.fishercoder.solutions;

/**
 * 1370. Increasing Decreasing String
 *
 * Given a string s. You should re-order the string using the following algorithm:
 * Pick the smallest character from s and append it to the result.
 * Pick the smallest character from s which is greater than the last appended character to the result and append it.
 * Repeat step 2 until you cannot pick more characters.
 * Pick the largest character from s and append it to the result.
 * Pick the largest character from s which is smaller than the last appended character to the result and append it.
 * Repeat step 5 until you cannot pick more characters.
 * Repeat the steps from 1 to 6 until you pick all characters from s.
 * In each step, If the smallest or the largest character appears more than once you can choose any occurrence and append it to the result.
 * Return the result string after sorting s with this algorithm.
 *
 * Example 1:
 * Input: s = "aaaabbbbcccc"
 * Output: "abccbaabccba"
 * Explanation: After steps 1, 2 and 3 of the first iteration, result = "abc"
 * After steps 4, 5 and 6 of the first iteration, result = "abccba"
 * First iteration is done. Now s = "aabbcc" and we go back to step 1
 * After steps 1, 2 and 3 of the second iteration, result = "abccbaabc"
 * After steps 4, 5 and 6 of the second iteration, result = "abccbaabccba"
 *
 * Example 2:
 * Input: s = "rat"
 * Output: "art"
 * Explanation: The word "rat" becomes "art" after re-ordering it with the mentioned algorithm.
 *
 * Example 3:
 * Input: s = "leetcode"
 * Output: "cdelotee"
 *
 * Example 4:
 * Input: s = "ggggggg"
 * Output: "ggggggg"
 *
 * Example 5:
 * Input: s = "spo"
 * Output: "ops"
 *
 * Constraints:
 * 1 <= s.length <= 500
 * s contains only lower-case English letters.
 * */
public class _1370 {
    public static class Solution1 {
        public String sortString(String s) {
            int[] count = new int[26];
            for (char c : s.toCharArray()) {
                count[c - 'a']++;
            }
            StringBuilder sb = new StringBuilder();
            while (sb.length() < s.length()) {
                for (int i = 0; i < count.length; i++) {
                    if (count[i] != 0) {
                        char character = (char) (i + 'a');
                        sb.append(character);
                        count[i]--;
                    }
                }
                for (int i = 25; i >= 0; i--) {
                    if (count[i] > 0) {
                        char character = (char) (i + 'a');
                        sb.append(character);
                        count[i]--;
                    }
                }
            }
            return sb.toString();
        }
    }
}