【算法导论】第八章之计数排序

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package com.zhoujie;

import java.util.Random;

/**
* heap sort
* @author zhoujie
*
*/
public class CountSort {
public static final int ARRAY_LENGTH = 10;
public static final int ARRAY_MAX_VALUE = 100;

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. count sort
int[] sortedArr = countSort(intArr);

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

private static int[] countSort(int[] intArr) {
int [] resultArr = new int[intArr.length];
int [] countArr = new int[ARRAY_MAX_VALUE + 1];
for(int i = 0; i < countArr.length; i++){
countArr[i] = 0;
}
for(int item : intArr){
countArr[item] = 1;
}
for(int i = 1; i < countArr.length ; i++){
countArr[i] = countArr[i-1] + countArr[i];
}
for(int i = intArr.length - 1; i >= 0; i--){
int index = countArr[intArr[i]]--;
resultArr[index - 1] = intArr[i];
}
return resultArr;
}

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());
}

}

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