解法一:

import java.util.*;
public class Solution {
    public void merge(int A[], int m, int B[], int n) {
        int i = 0,j = 0,k = 0;//定义指针
        int [] C = new int [m + n]; 
        while(i < m && j < n){
            if(A[i]<B[j]){
                C[k++]=A[i++];
            }else{
                C[k++]=B[j++];
            }
        }
        while(i < m){
            C[k++]=A[i++];
        }
        while(j < n){
            C[k++]=B[j++];
        }
        for(int u = 0;u < m+n;u++){
            A[u]=C[u];
        }
    }
}

解法二:

import java.util.*;
public class Solution {
    public void merge(int A[], int m, int B[], int n) {
        int i = m-1,j = n-1,k = m+n-1;//定义指针
        //从最大的开始遍历
        while(i >= 0&& j>=0){
            if(A[i]>B[j]){
                A[k--]=A[i--];
            }else{
                A[k--]=B[j--];
            }
        }
        while(i >= 0){
            A[k--] = A[i--];   
        }
        while(j >= 0){
            A[k--] = B[j--];
        }
    }
}