【算法导论】第八章之基数排序

asdfas

package com.zhoujie;

import java.util.ArrayList;
import java.util.List;
import java.util.Map;
import java.util.Random;
import java.util.TreeMap;

public class RadixSort {
	public static final int ARRAY_LENGTH = 10;
	public static final int ARRAY_MAX_VALUE = 1000;

	public static final String LOG_PREFIX = "=====================";
	public static final String LOG_SUFFIX = LOG_PREFIX;
	public static final String ARR_DELIMITER = "\t";

	public static void main(String[] args) {
		// 1. generate input array
		Random random = new Random();

		int[] intArr = new int[ARRAY_LENGTH];
		printLine(LOG_PREFIX + "The original array is:" + LOG_SUFFIX);
		for (int i = 0; i < intArr.length; i++) {
			intArr[i] = random.nextInt(ARRAY_MAX_VALUE);
			print(intArr[i]);
			if (i != intArr.length - 1) {
				print(ARR_DELIMITER);
			}
		}
		printLine("");

		// 2. radix sort
		radixSort(intArr);

		// 3. print sorted array
		printLine(LOG_PREFIX + "The sorted array is:" + LOG_SUFFIX);
		printLine(join(intArr, ARR_DELIMITER));
	}

	private static void radixSort(int[] intArr) {
		int maxDigits = String.valueOf(ARRAY_MAX_VALUE).length();
		for(int i = 1; i <= maxDigits; i ++){
			sortByDigit(intArr, i);
		}
	}

	private static void sortByDigit(int[] intArr, int i) {
		Map> map = new TreeMap>();
		for(int item : intArr){
			int digit = getDigit(item, i);
			List list = map.get(digit);
			if(list == null){
				list = new ArrayList();
				map.put(digit, (ArrayList) list);
			}
			list.add(item);
		}
		int index = 0;
		for(int key : map.keySet()){
			List list = map.get(key);
			for(int item : list){
				intArr[index++] = item;
			}
		}
	}

	private static int getDigit(int item, int i) {
		StringBuilder sb = new StringBuilder(String.valueOf(item));
		String reverseStr = sb.reverse().toString();
		if(reverseStr.length() >= i){
			return Integer.valueOf(reverseStr.charAt(i-1));
		} else {
			return 0;
		}
	}

	public static void print(Object t) {
		System.out.print(t);
	}

	public static void printLine(Object t) {
		System.out.println(t);
	}

	public static String join(int[] arr, String delimiter) {
		StringBuilder sb = new StringBuilder();
		for (int element : arr) {
			sb.append(element);
			sb.append(delimiter);
		}
		return sb.substring(0, sb.length());
	}

}

alsdlfs