算法(Algorithms)第4版 练习 2.1.25
代码实现:
package com.qiusongde; import edu.princeton.cs.algs4.In; import edu.princeton.cs.algs4.StdOut; public class InsertionHalfExchange { public static void sort(Comparable[] a) { int N = a.length; for(int i = 1; i < N; i++) { Comparable temp = a[i]; int j = i; while(j > 0 && less(temp, a[j-1])) { a[j] = a[j-1]; j--; } a[j] = temp; // show(a); } } private static boolean less(Comparable v, Comparable w) { return v.compareTo(w) < 0; } private static void exch(Comparable[] a, int i, int j) { Comparable t = a[i]; a[i] = a[j]; a[j] = t; } private static void show(Comparable[] a) { //print the array, on a single line. for(int i = 0; i < a.length; i++) { StdOut.print(a[i] + " "); } StdOut.println(); } public static boolean isSorted(Comparable[] a) { for(int i = 1; i < a.length; i++) { if(less(a[i], a[i-1])) return false; } return true; } public static void main(String[] args) { //Read strings from standard input, sort them, and print. String[] a = In.readStrings(); show(a); sort(a); assert isSorted(a); show(a); } }
单元测试结果:
S O R T E X A M P L E
O S R T E X A M P L E
O R S T E X A M P L E
O R S T E X A M P L E
E O R S T X A M P L E
E O R S T X A M P L E
A E O R S T X M P L E
A E M O R S T X P L E
A E M O P R S T X L E
A E L M O P R S T X E
A E E L M O P R S T X
A E E L M O P R S T X
比较Insertion和InsertionHalfExchange 的性能:
package com.qiusongde; import edu.princeton.cs.algs4.Shell; import edu.princeton.cs.algs4.StdOut; import edu.princeton.cs.algs4.StdRandom; public class SortCompare { public static double timeRandomInput(String alg, int N, int T) { double total = 0.0; Double[] a = new Double[N]; for(int t = 0; t < T; t++) { for(int i = 0; i < N; i++) a[i] = StdRandom.uniform(); total += time(alg, a); } return total; } public static double time(String alg, Double[] a) { Stopwatch timer = new Stopwatch(); if(alg.equals("Selection")) Selection.sort(a); if(alg.equals("Insertion")) Insertion.sort(a); if(alg.equals("InsertionHalfExchange")) InsertionHalfExchange.sort(a); if(alg.equals("Shell")) Shell.sort(a); return timer.elapsedTime(); } public static void main(String[] args) { String alg1 = "Insertion"; String alg2 = "InsertionHalfExchange"; int N = 1000; int T = 1000; double t1 = timeRandomInput(alg1, N, T); double t2 = timeRandomInput(alg2, N, T); StdOut.printf("For %d random Doubles %d trials\n", N, T, alg1); StdOut.printf("%s is %.1fs %s is %.1fs", alg1, t1, alg2, t2); } }
For 1000 random Doubles 1000 trials
Insertion is 1.1s InsertionHalfExchange is 0.5s