标签：static get com fast ret merge ati out imp
关键代码实现：
public static void sort(Comparable[] input) { int N = input.length; aux = input.clone();//must be clone(the same as input) // StdOut.println("input:" + input + " aux:" + aux);//for test sort(aux, input, 0, N-1); } //take input from source, sort it and put output in destination //source and destination is the same at the beginning private static void sort(Comparable[] source, Comparable[] destination, int lo, int hi) { if(lo >= hi)//just one entry in array return; int mid = lo + (hi-lo)/2; sort(destination, source, lo, mid);//first get input from destination, sort it and put output in source sort(destination, source, mid+1, hi); merge(source, destination, lo, mid, hi);//merge sorted source to destination } private static void merge(Comparable[] source, Comparable[] destination, int lo, int mid, int hi) { int i = lo; int j = mid + 1; for(int k = lo; k <= hi; k++) { if(i > mid) destination[k] = source[j++]; else if(j > hi) destination[k] = source[i++]; else if(less(source[j], source[i])) destination[k] = source[j++]; else destination[k] = source[i++]; } // StdOut.println("source:" + source + " destination:" + destination); // StdOut.printf("merge(source, destination, %4d, %4d, %4d)", lo, mid, hi); // show(destination);//for test }
测试用例：
package com.qiusongde; import edu.princeton.cs.algs4.In; import edu.princeton.cs.algs4.StdOut; public class MergeAvoidCopy { private static Comparable[] aux; public static void sort(Comparable[] input) { int N = input.length; aux = input.clone();//must be clone(the same as input) // StdOut.println("input:" + input + " aux:" + aux);//for test sort(aux, input, 0, N-1); } //take input from source, sort it and put output in destination //source and destination is the same in start private static void sort(Comparable[] source, Comparable[] destination, int lo, int hi) { if(lo >= hi)//just one entry in array return; int mid = lo + (hi-lo)/2; sort(destination, source, lo, mid);//first get input from destination, sort it and put output in source sort(destination, source, mid+1, hi); merge(source, destination, lo, mid, hi);//merge sorted source to destination } private static void merge(Comparable[] source, Comparable[] destination, int lo, int mid, int hi) { int i = lo; int j = mid + 1; for(int k = lo; k <= hi; k++) { if(i > mid) destination[k] = source[j++]; else if(j > hi) destination[k] = source[i++]; else if(less(source[j], source[i])) destination[k] = source[j++]; else destination[k] = source[i++]; } // StdOut.println("source:" + source + " destination:" + destination); // StdOut.printf("merge(source, destination, %4d, %4d, %4d)", lo, mid, hi); // show(destination);//for test } private static boolean less(Comparable v, Comparable w) { return v.compareTo(w) < 0; } 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[] input = In.readStrings(); // show(input);//for test sort(input); assert isSorted(input); // show(input);//for test } }
测试结果：
M E R G E S O R T E X A M P L E input:[Ljava.lang.String;@1b6d3586 aux:[Ljava.lang.String;@4554617c source:[Ljava.lang.String;@1b6d3586 destination:[Ljava.lang.String;@4554617c merge(source, destination, 0, 0, 1)E M R G E S O R T E X A M P L E source:[Ljava.lang.String;@1b6d3586 destination:[Ljava.lang.String;@4554617c merge(source, destination, 2, 2, 3)E M G R E S O R T E X A M P L E source:[Ljava.lang.String;@4554617c destination:[Ljava.lang.String;@1b6d3586 merge(source, destination, 0, 1, 3)E G M R E S O R T E X A M P L E source:[Ljava.lang.String;@1b6d3586 destination:[Ljava.lang.String;@4554617c merge(source, destination, 4, 4, 5)E M G R E S O R T E X A M P L E source:[Ljava.lang.String;@1b6d3586 destination:[Ljava.lang.String;@4554617c merge(source, destination, 6, 6, 7)E M G R E S O R T E X A M P L E source:[Ljava.lang.String;@4554617c destination:[Ljava.lang.String;@1b6d3586 merge(source, destination, 4, 5, 7)E G M R E O R S T E X A M P L E source:[Ljava.lang.String;@1b6d3586 destination:[Ljava.lang.String;@4554617c merge(source, destination, 0, 3, 7)E E G M O R R S T E X A M P L E source:[Ljava.lang.String;@1b6d3586 destination:[Ljava.lang.String;@4554617c merge(source, destination, 8, 8, 9)E E G M O R R S E T X A M P L E source:[Ljava.lang.String;@1b6d3586 destination:[Ljava.lang.String;@4554617c merge(source, destination, 10, 10, 11)E E G M O R R S E T A X M P L E source:[Ljava.lang.String;@4554617c destination:[Ljava.lang.String;@1b6d3586 merge(source, destination, 8, 9, 11)E G M R E O R S A E T X M P L E source:[Ljava.lang.String;@1b6d3586 destination:[Ljava.lang.String;@4554617c merge(source, destination, 12, 12, 13)E E G M O R R S E T A X M P L E source:[Ljava.lang.String;@1b6d3586 destination:[Ljava.lang.String;@4554617c merge(source, destination, 14, 14, 15)E E G M O R R S E T A X M P E L source:[Ljava.lang.String;@4554617c destination:[Ljava.lang.String;@1b6d3586 merge(source, destination, 12, 13, 15)E G M R E O R S A E T X E L M P source:[Ljava.lang.String;@1b6d3586 destination:[Ljava.lang.String;@4554617c merge(source, destination, 8, 11, 15)E E G M O R R S A E E L M P T X source:[Ljava.lang.String;@4554617c destination:[Ljava.lang.String;@1b6d3586 merge(source, destination, 0, 7, 15)A E E E E G L M M O P R R S T X A E E E E G L M M O P R R S T X
性能比较：
For 20000 random Doubles 1000 trials Merge is 3.4s MergeFasterM is 3.1s MergeUseInsert is 3.2s MergeSkipMerge is 3.3s MergeAvoidCopy is 3.0s
算法（Algorithms）第4版 练习 2.2.11（3）
标签：static get com fast ret merge ati out imp
原文地址：http://www.cnblogs.com/songdechiu/p/6613514.html
