合并数组（升序数组降序合并，反之）

1.首先不管是升序还是降序，反向排，所以数组下标都从最后开始

2.升序降序的不同只有两数比较时不同（max min）

import java.util.*;
public class main1 {
    public static void main(String[] args) {
        int[]A={0,-2};
        int[]B={10,0,-1};
        int len = A.length + B.length;
        int[] ret = new int[len];
        int index = 0;
        if (A.length == 0) {
            for (int i = B.length - 1; i >= 0; i--) {
                ret[index++] = B[i];
            }
            System.out.println(Arrays.toString(ret));
        }
        if (B.length == 0) {
            for (int i = A.length - 1; i >= 0; i--) {
                ret[index++] = A[i];
            }
            System.out.println(Arrays.toString(ret));
        }
        if (A.length == 0 && B.length == 0)
            System.out.println(Arrays.toString(ret));
        int index1 = A.length - 1;
        int index2 = B.length - 1;
        if (A[0] > A[1]) {//降序排升序
            while (index1 >= 0 && index2 >= 0) {
                if (A[index1] < B[index2]) {
                    ret[index++] = A[index1--];
                } else {
                    ret[index++] = B[index2--];
                }
            }
            if (index1 >= 0) {
                ret[index++] = A[index1--];
            }
            if (index2 >= 0) {
                ret[index++] = B[index2--];
            }
            System.out.println(Arrays.toString(ret));
        } else {//升序排降序
            while (index1 >= 0 && index2 >= 0) {
                if (A[index1] > B[index2]) {
                    ret[index++] = A[index1--];
                } else {
                    ret[index++] = B[index2--];
                }
            }
            if (index1 >=0) {
                ret[index++] = A[index1--];
            }
            if (index2 >= 0) {
                ret[index++] = B[index2--];
            }
            System.out.println(Arrays.toString(ret));
        }
    }


}