伪代码

MERGE(A,p,q,r) n1=q-p+1; n2=r-q; create new arrays L[n1+1] and R[n2+1] for i=0 to n1-1 L[i]=A[p+i] for j=0 to n2-1 R[j]=A[q+1+j] L[n1]=1000//假设1000是无穷大 R[n2]=1000 i=j=0 for k=p to r if(L[i]<=R[j]) A[k]=L[i] i=i+1 else A[k]=R[j] j=j+1 MERGE_SORT(A,p,r) if p<r q=floor((p+r)/2) MERGE_SORT(A,p,q) MERGE_SORT(A,q+1,r) MERGE(A,p,q,r)

c实现

void main(){
    int A[]={3,8,1,4,5,0,2,5};
    int i;
    int len=sizeof(A)/sizeof(A[0]);
    merge_sort(A,0,7);
    for(i=0;i<len;i++){
        printf("%d ",A[i]);
    }
}
void merge(int A[],int p,int q,int r){
    int n1,n2,i,j,k;
    n1=q-p+1;
    n2=r-q;
    int L[n1+1];
    int R[n2+1];
    for(i=0;i<n1;i++){
        L[i]=A[p+i];
    }
    for(j=0;j<n2;j++){
        R[j]=A[q+j+1];
    }
    L[n1]=1000;//假设100是无穷大的数
    R[n2]=1000;
    i=0;
    j=0;
    for(k=p;k<=r;k++){
        if(L[i]<=R[j]){
            A[k]=L[i];
            i=i+1;
        }else{
            A[k]=R[j];
            j=j+1;
        }
    }
}
void merge_sort(int A[],int p,int r){
    int q;
    if(p<r){
        q=floor((p+r)/2);
        merge_sort(A,p,q);
        merge_sort(A,q+1,r);
        merge(A,p,q,r);
    }
}

java实现

public class Main {

    public static void main(String[] args) {
        int [] arr={3,8,1,4,5,0,2,5};
        merge_sort(arr,0,7);
        for(int i=0;i<arr.length;i++)
            System.out.print(arr[i]+" ");
    }
    public static void merge(int [] arr,int p,int q,int r){
        int len1=q-p+1;
        int len2=r-q;
        int [] arrLeft=new int[len1+1];
        int [] arrRight=new int[len2+1];
        for(int i=0;i<len1;i++){
            arrLeft[i]=arr[p+i];
        }
        for(int j=0;j<len2;j++){
            arrRight[j]=arr[q+1+j];
        }
        arrLeft[len1]=1000;
        arrRight[len2]=1000;
        int i=0;
        int j=0;
        for(int k=p;k<=r;k++){
            if(arrLeft[i]<=arrRight[j]){
                arr[k]=arrLeft[i];
                i++;
            }else{
                arr[k]=arrRight[j];
                j++;
            }
        }
    }
    public static void merge_sort(int [] arr,int p,int r){
        if(p<r){
            int q=(int)Math.floor((p+r)/2);
            merge_sort(arr,p,q);
            merge_sort(arr,q+1,r);
            merge(arr,p,q,r);
        }
    }
}