算法 第四章 2.2.9 | 2.2.11

package Cap2_2;import edu.princeton.cs.introcs.StdOut;import edu.princeton.cs.introcs.StdRandom;import Cap2_1.Insertion;import Cap2_1.sortTemplate;public class MergeModify extends sortTemplate{public static void sort(Comparable[] a){Comparable[] aux = a.clone();sort(a, aux, 0, a.length-1, true);}private static void sort(Comparable[] a, Comparable[] aux, int lo, int hi, boolean ok){ //自顶向下if(hi-lo<=10) {  //优化1Insertion.sort(a, lo, hi);return;}if(hi<=lo) return;int mid = lo + (hi-lo)/2;sort(a, aux, lo, mid, !ok);sort(a, aux, mid+1, hi, !ok);//if(less(a[mid], a[mid+1])) return;  //优化2 无法使用，因为每次必须交换两个数组，必须要mergeif(ok) merge(a, aux, lo, mid, hi);  //优化3 交替使用两个数组else   merge(aux, a, lo, mid, hi); }public static void merge(Comparable[] a, Comparable[] aux, int lo, int mid, int hi){ // aux --> aint i=lo, j=mid+1;for(int k=lo;k<=hi;k++){if      (i>mid)                a[k]=aux[j++];else if (j>hi)                 a[k]=aux[i++];else if (less(aux[i], aux[j])) a[k]=aux[i++];else                           a[k]=aux[j++];}}public static void main(String[] args) {int N = 500;Integer[] a = new Integer[N];for(int j=0;j<N;j++)a[j]=j;StdRandom.shuffle(a);show(a);sort(a);show(a);assert isSorted(a);}}