【算法导论】第七章之快速排序

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package com.zhoujie;import java.util.Random;public class QuickSort {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 arrayRandom 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. quick sortquickSort(intArr);// 3. print sorted arrayprintLine(LOG_PREFIX + "The sorted array is:" + LOG_SUFFIX);printLine(join(intArr, ARR_DELIMITER));}public static void quickSort(int[] intArr) {quickSort(intArr, 0, (intArr.length-1));}private static void quickSort(int[] intArr, int i, int j) {int keyPoint = partition(intArr, i, j);if(i != keyPoint){quickSort(intArr, i, keyPoint-1);}if(j != keyPoint){quickSort(intArr, keyPoint+1, j);}}private static int partition(int[] intArr, int start, int end) {int keyWordValue = intArr[end];int shouldPos = start;/* * shouldPos在for循环中应该满足循环不变式 * shouldPos:  * 1. 在shouldPos（不包括它自己）之前的所有数据都小于等于keykeyWordValue * 2. 在shouldPos（包括它自己）之后的所有数据都大于keykeyWordValue */for(int i = start; i < end; i ++){if(intArr[i] > keyWordValue){// nothing to do} else {if(shouldPos != i){swap(intArr, shouldPos, i);}shouldPos ++;}}swap(intArr, shouldPos, end);return shouldPos;}private static void swap(int[] intArr, int i, int j) {int temp = intArr[j];intArr[j] = intArr[i];intArr[i] = temp;}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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