合并两个有序数组

题目：有两个排序的数组arr1和arr2，内存在arr1的末尾有足够的空余空间容纳arr2，实现一个函数，把arr2中的所有数字插入到arr1中，并且所有的数字是排序的
思路：从后向前合并

#include<iostream>
using namespace std;

int* MergeTwoArr(int *arr1, int *arr2, int len1, int len2)
{
    if (arr1 == NULL)
        return arr2;
    if (arr2 == NULL)
        return arr1;
    int len = len1 + len2 - 1;
    int i = len1 - 1, j = len2 - 1;
    while (i >= 0 && j >= 0)
    {
        if (arr2[j] > arr1[i])
        {
            arr1[len--] = arr2[j--];
        }
        else if (arr2[j] < arr1[i])
        {
            arr1[len--] = arr1[i--];
        }
        else
        {
            arr1[len--] = arr1[i--];
            arr1[len--] = arr2[j--];
        }
    }
    if (i >= 0)
    {
        for (; i >= 0; i--)
        {
            arr1[len--] = arr1[i--];
        }
    }
    if (j >= 0)
    {
        for (; j >= 0; j--)
        {
            arr1[len--] = arr2[j--];
        }
    }
    return arr1;
}

int main()
{
    int arr1[1024] = { 1, 2, 5, 7, 8, 9 };
    int arr2[] = { 0, 2, 3, 4, 6, 7,11 ,13};
    int len1 = 1;
    for (int i = 0; i < 1024; i++)
    {
        if (arr1[i] < arr1[i + 1])
            len1++;
        else
            break;
    }
    int len2 = sizeof(arr2) / sizeof(arr2[0]);

    int *arr = MergeTwoArr(arr1, arr2, len1, len2);
    for (int i = 0; i < len1 + len2; i++)
    {
        cout << arr[i] << " ";
    }
    cout << endl;
    getchar();
    return 0;
}