题解 | 字符统计|构造有序链表

import java.io.*;
import java.util.*;

class Node {
    char ch;
    int count;
    Node next;

    Node(char ch, int count) {
        this.ch = ch;
        this.count = count;
    }

    Node() {

    }
}


// 注意类名必须为 Main, 不要有任何 package xxx 信息
public class Main {
    public static void main(String[] args) throws Exception {
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        String s = br.readLine();
        br.close();

        int[] arr = new int[26];
        int[] narr = new int[10];

        for (int i = 0; i < s.length(); i++) {
            char ch = s.charAt(i);
            if (Character.isDigit(ch)) {
                narr[ch - '0']++;
            } else {
                arr[ch - 'a']++;
            }
        }
        Node dummy = new Node();

        buildList(dummy, narr, true);
        buildList(dummy, arr, false);

        Node cursor = dummy.next;
        while (cursor != null) {
            System.out.print(cursor.ch);
            cursor = cursor.next;
        }
    }

    public static void buildList(Node dummy, int[] arr, boolean isDigit) {
        for (int i = 0; i < arr.length; i++) {
            if (arr[i] != 0) {
                Node cursor = dummy.next;
                Node prev = dummy;
                int k = isDigit ? '0' : 'a';
                Node t = new Node((char)(i + k), arr[i]);
                while (cursor != null) {
                    if (cursor.count < arr[i]) {
                        t.next = cursor;
                        prev.next = t;
                        break;
                    }
                    prev = cursor;
                    cursor = cursor.next;
                }
                if (cursor == null) {
                    prev.next = t;
                }
            }
        }
    }
}