［算法之排序］快速排序算法（java实现）

来源：互联网发布：室内设计好的软件编辑：程序博客网时间：2024/06/11 21:17
/*** *  * @author xiaoo_gan * 快速排序 *  *  * 测试： * 第一种partition * 排序 20000000 个数, 快速排序用时: 11.58600 秒 * 排序 50000000 个数, 快速排序用时: 37.75700 秒 *  *  * 第二种partition * 排序 20000000 个数, 快速排序用时: 12.05800 秒 *  */public class Quick {//第一种排序public static void sort(Comparable[] a) {//StdRandom.shuffle(a);sort(a, 0, a.length -1);}private static void sort(Comparable[] a, int lo, int hi) {if(hi <= lo)return;int j = partition(a, lo, hi);sort(a, lo, j - 1);sort(a, j + 1, hi);}//partiton函数一private static int partition(Comparable[] a, int lo, int hi) {int i = lo;int j = hi + 1;Comparable value = a[lo];while(true) {while(less(a[++i], value))if (i == hi) {break;}while(less(value, a[--j]))if (j == lo) {break;}if (i >= j) {break;}exch(a, i, j);}exch(a, lo, j);return j;}private static boolean less(Comparable a, Comparable b) {return (a.compareTo(b) < 0);}//第二种排序public static void sort1(Comparable[] a) {//StdRandom.shuffle(a);sort1(a, 0, a.length -1);}private static void sort1(Comparable[] a, int lo, int hi) {if(hi <= lo)return;int j = partition1(a, lo, hi);sort(a, lo, j - 1);sort(a, j + 1, hi);}//partiton函数二 来自算法导论private  static int partition1(Comparable[] a, int lo, int hi) {Comparable x = a[hi];int i = lo - 1;for (int j = lo; j <= hi - 1; j++) {if (less1(a[j], x)) {i ++;exch(a, i, j);}}exch(a, i + 1, hi);return i + 1;}private static boolean less1(Comparable a, Comparable b) {return (a.compareTo(b) <= 0);}private static void exch(Comparable[] a, int i, int j) {Comparable swap = a[i];a[i] = a[j];a[j] = swap;}public static boolean isSorted(Comparable[] a) {for (int i = 0; i < a.length - 1; i++) {if(!less(a[i], a[i+1]))return false;}return true;}private static void print(Boolean isSorted, Comparable[] a) {if (isSorted) {StdOut.println("after sorting :");} else {StdOut.println("before sorting :");}for (int i = 0; i < a.length; i++) {if ((i % 10) == 0) {if(i != 0)StdOut.println();StdOut.print("\t");}StdOut.print("\t" + a[i]);}StdOut.println();}public static void main(String[] args) {int M = 20000000;Double[] a = new Double[M];for (int i = 0; i < M; i++) {a[i] = StdRandom.uniform();}//String[] a = {"S", "O", "R", "T", "E", "X", "A", "M", "P", "L", "E"};//print(false, a);Stopwatch timer = new Stopwatch();sort1(a);double elapsedTime = timer.elapsedTime();//print(true, a);if(isSorted(a))System.out.printf("排序 %d 个数, 快速排序用时: %.5f 秒", a.length, elapsedTime);}}
0 0