分治法处理排序问题

 1、二分检索：

package divideAndConquer;

public class BINSRCH {
    int j=-1;
    BINSRCH(){
        int[] a={4,7,3,1,5,6,0,8,9,2};
        binsrch(a,10,5);//binsrch(a,10,5,j),这样不可以，java传给参数的只是引用，函数改变参数参数，在外面看不到变化
        System.out.println(j);
    }
    public void binsrch(int[] A,int n,int x){
        int low,high,mid;
        low=0;
        high=n-1;
        while(low<=high){
            mid=(low+high)/2;
            if(A[mid]==x){
                j=mid;
                return;
            }
            else{
                if(A[mid]<x){
                    low=mid+1;
                }else{
                    high=mid-1;
                }
            }
        }        
    }
    public static void main(String[] args) {
        // TODO Auto-generated method stub
        new BINSRCH();
    }

}

2、分治法对数组a={2,4,67,8,98,44,2,344,43,3,4,4,3,4,3}排序（非降）

package divideAndConquer;

import java.lang.reflect.Array;

public class MERGE {
    int[] a={2,4,67,8,98,44,2,344,43,3,4,4,3,4,3};
    int n=Array.getLength(a);
    MERGE(){
        danc(0,n-1);
        //selectSort(0,n-1);
        System.out.print("分治法排序结果：");
        for(int i=0;i<n;i++){
            System.out.print(a[i]+" ");
        }
    }
    public void danc(int low,int high){
        int mid=(low+high)/2;
        if(high-low<5){
            selectSort(low,high);
            return;    
        }
        danc(low,mid);
        danc(mid+1,high);
        merge(low,mid,high);

    }
    public void selectSort(int low,int high){
        int temp;
        for(int i=low+1;i<=high;i++){
            temp=a[i];
            int j=i;
            while(temp<a[j-1]&&j>low){//这里一定要加上  j>low 防止越界
                a[j]=a[j-1];
                j--;
            }
            a[j]=temp;
        }
    }
    public void merge(int low,int mid,int high){
        int[] b=new int[high-low+1];
        int i=low;
        int j=mid+1;
        int k=0;
        while(i<=mid&&j<=high){
            if(a[i]<=a[j]){
                b[k]=a[i];
                i++;
                k++;
            }else{
                b[k]=a[j];
                j++;
                k++;
            }
        }
        if(i<=mid){
            for(;i<=mid;i++){
                b[k]=a[i];
                k++;
            }
        }else
            for(;j<=high;j++){
                b[k]=a[j];
                k++;
            }
        for(i=0;i<high-low+1;i++){
            a[low+i]=b[i];
        }
    }
    public static void main(String[] args) {
        // TODO Auto-generated method stub
        new MERGE();
    }

}

调试代码：

package divideAndConquer;

import java.lang.reflect.Array;

public class MERGE {
    int[] a={2,4,67,8,98,44,2,344,43,3,4,4,3,4,3};
    int n=Array.getLength(a);
    MERGE(){
        System.out.println(n);
        danc(0,n-1);
        //selectSort(0,n-1);
        System.out.print("分治法排序结果：");
        for(int i=0;i<n;i++){
            System.out.print(a[i]+" ");
        }
    }
    public void danc(int low,int high){
        int mid=(low+high)/2;
        if(high-low<5){
            selectSort(low,high);
            return;    
        }
        System.out.print("划分子集 成:");
        for(int i=low;i<=high;i++){
            if(i==mid+1)
                System.out.print("   ");
            System.out.print(a[i]+" ");
        }
        System.out.println();
        danc(low,mid);
        danc(mid+1,high);
        merge(low,mid,high);

    }
    public void selectSort(int low,int high){
        System.out.println("选择排序处理："+low+"-到-"+high+"号元素");
for(int i=0;i<n;i++){
            
            System.out.print(a[i]+"..");
        }
        System.out.println();
        int temp;
        for(int i=low+1;i<=high;i++){
            temp=a[i];
            int j=i;
            while(temp<a[j-1]&&j>low){//这里一定要加上  j>low 防止越界
                a[j]=a[j-1];
                j--;
            }
            a[j]=temp;
        }
    for( int i=low;i<=high;i++){
            
            System.out.print(a[i]+"*");
        }
        System.out.println();
    }
    public void merge(int low,int mid,int high){
        System.out.println("合并："+low+"+"+mid+"+"+high);
        int[] b=new int[high-low+1];
        int i=low;
        int j=mid+1;
        int k=0;
        while(i<=mid&&j<=high){
            if(a[i]<=a[j]){
                b[k]=a[i];
                i++;
                k++;
            }else{
                b[k]=a[j];
                j++;
                k++;
            }
        }
        if(i<=mid){
            for(;i<=mid;i++){
                b[k]=a[i];
                k++;
            }
        }else
            for(;j<=high;j++){
                b[k]=a[j];
                k++;
            }
        for(i=0;i<high-low+1;i++){
            a[low+i]=b[i];
        }
        for( i=low;i<=high;i++){
            
            System.out.print(a[i]+" ");
        }
        System.out.println();
        System.out.print("此时整个a数组状态:");
for( i=0;i<n;i++){
            
            System.out.print(a[i]+"..");
        }
        System.out.println();
    }
    public static void main(String[] args) {
        // TODO Auto-generated method stub
        new MERGE();
    }

}