第五天算法设计

归并排序
需求：
排序前：{8,4,5,7,1,3,6,2}
排序后：{1,2,3,4,5,6,7,8}
算法设计
Merge类：
package suanfa;

public class Merge {
private static Comparable[] assist;
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;
}

public static void sort(Comparable[] a){
    assist = new Comparable[a.length];

    int lo=0;
    int hi=a.length-1;
    sort(a,lo,hi);
}
private static void sort(Comparable[] a,int lo,int hi){
    if(hi<= lo){
        return;
    }

    int mid = lo+(hi-lo)/2;
    sort(a,lo,mid);
    sort(a,mid+1,hi);
    merge(a,lo,mid,hi);
}
private static void merge(Comparable[] a,int lo,int mid,int hi){

    int i =lo;
    int p1 =lo;
    int p2 =mid+1;

    while(p1<=mid&&p2<=hi) {
        if (less(a[p1], a[p2])) {
            assist[i++] = a[p1++];
        } else {
            assist[i++] = a[p2++];
        }
    }
        while (p1<=mid){
            assist[i++]=a[p1++];
        }
        while (p2<=hi){
            assist[i++]=a[p2++];
        }
        for(int index=lo;index<=hi;index++){
            a[index]=assist[index];
        }



}

}
MergeTest类：
package suanfa;

import java.util.Arrays;

public class MergeTest {
public static void main(String[] args) {
Integer[] a={8,4,5,7,1,3,6,2};
Merge.sort(a);
System.out.println(Arrays.toString(a));
}
}

录制: untitled2 – Merge.java
录制文件：https://meeting.tencent.com/crm/K0oDw6L726