_1417.java

package com.fishercoder.solutions;

import java.util.ArrayList;
import java.util.List;

/**
 * 1417. Reformat The String
 *
 * Given alphanumeric string s. (Alphanumeric string is a string consisting of lowercase English letters and digits).
 * You have to find a permutation of the string where no letter is followed by another letter and no digit is followed by another digit.
 * That is, no two adjacent characters have the same type.
 * Return the reformatted string or return an empty string if it is impossible to reformat the string.
 *
 * Example 1:
 * Input: s = "a0b1c2"
 * Output: "0a1b2c"
 * Explanation: No two adjacent characters have the same type in "0a1b2c". "a0b1c2", "0a1b2c", "0c2a1b" are also valid permutations.
 *
 * Example 2:
 * Input: s = "leetcode"
 * Output: ""
 * Explanation: "leetcode" has only characters so we cannot separate them by digits.
 *
 * Example 3:
 * Input: s = "1229857369"
 * Output: ""
 * Explanation: "1229857369" has only digits so we cannot separate them by characters.
 *
 * Example 4:
 * Input: s = "covid2019"
 * Output: "c2o0v1i9d"
 *
 * Example 5:
 * Input: s = "ab123"
 * Output: "1a2b3"
 *
 * Constraints:
 * 1 <= s.length <= 500
 * s consists of only lowercase English letters and/or digits.
 * */
public class _1417 {
    public static class Solution1 {
        public String reformat(String s) {
            List<Character> characterList = new ArrayList<>();
            List<Character> numberList = new ArrayList<>();
            for (char c : s.toCharArray()) {
                if (Character.isAlphabetic(c)) {
                    characterList.add(c);
                } else {
                    numberList.add(c);
                }
            }
            if (Math.abs(characterList.size() - numberList.size()) > 1) {
                return "";
            } else {
                StringBuilder sb = new StringBuilder();
                if (characterList.size() > numberList.size()) {
                    for (int i = 0; i < characterList.size() - 1; i++) {
                        sb.append(characterList.get(i));
                        sb.append(numberList.get(i));
                    }
                    sb.append(characterList.get(characterList.size() - 1));
                } else if (characterList.size() == numberList.size()) {
                    for (int i = 0; i < numberList.size(); i++) {
                        sb.append(numberList.get(i));
                        sb.append(characterList.get(i));
                    }
                } else {
                    for (int i = 0; i < numberList.size() - 1; i++) {
                        sb.append(numberList.get(i));
                        sb.append(characterList.get(i));
                    }
                    sb.append(numberList.get(numberList.size() - 1));
                }
                return sb.toString();
            }
        }
    }
}