【算法导论】第六章之堆排序

package com.zhoujie;

import java.util.Random;

/**
* Heap Sort
* @author zhoujie
*/
public class HeapSort {
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";

private static int heapSize = ARRAY_LENGTH;

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. insert sort
heapSort(intArr);

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

public static void heapSort(int[] intArr) {
buildMaxHeap(intArr);
for (int i = intArr.length - 1; i > 0; i--) {
swap(intArr, 0, i);
heapSize--;
maxHeapify(intArr, 0);
}
}

private static void swap(int[] intArr, int i, int j) {
int temp = intArr[j];
intArr[j] = intArr[i];
intArr[i] = temp;
}

private static void maxHeapify(int[] intArr, int i) {
int leftIndex = leftChildIndex(i);
int rightIndex = rightChildIndex(i);
int largest = i;
if (leftIndex <= (heapSize - 1) && intArr[leftIndex] > intArr[i]) {
largest = leftIndex;
} else {
largest = i;
}

if (rightIndex <= (heapSize - 1) && intArr[rightIndex] > intArr[largest]) {
largest = rightIndex;
}
if (largest != i) {
swap(intArr, i, largest);
maxHeapify(intArr, largest);
}
}

private static int rightChildIndex(int i) {
return (2 * i + 2);
}

private static int leftChildIndex(int i) {
return (2 * i + 1);
}

private static void buildMaxHeap(int[] intArr) {
heapSize = intArr.length;
for (int i = intArr.length / 2; i >= 0; i--) {
maxHeapify(intArr, i);
}
}

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());
}

}