leetCode上刷题碰到的问题，Create Maximum Number

Question

这是题目的网址，感兴趣可以去试试 ： 原题网址

题目 :

Given two arrays of length m and n with digits 0-9 representing two
numbers. Create the maximum number of length k <= m + n from digits of
the two. The relative order of the digits from the same array must be
preserved. Return an array of the k digits. You should try to optimize
your time and space complexity.

Example 1: nums1 = [3, 4, 6, 5] nums2 = [9, 1, 2, 5, 8, 3] k = 5
return [9, 8, 6, 5, 3]

Example 2: nums1 = [6, 7] nums2 = [6, 0, 4] k = 5 return [6, 7, 6, 0,
4]

Example 3: nums1 = [3, 9] nums2 = [8, 9] k = 3 return [9, 8, 9]

网上我搜索了很久都没有搜索到C语言的答案，自己写了一个答案但是没用过不了，我和这个人碰到了一样的问题，这里是这个人问题的链接。。想问问是我理解题目有问题还是怎么，难道它不是要我返回一个指针吗？

Answer 1

据我观察你的链接里那位哥们没有给参数 returnsize赋值，所以调用端并不知道它的int数组长度，你可以检查下你的代码是否是同样的问题。

Answer 2

这个问题我只能想出O(nk)的算法，写完之后直接去交，遇到了跟题主一样的问题，然后查了下其他题目的代码，发现要将returnSize赋值成那个数组的大小。。。下面上代码：

 int* calc(int* nums,int n,int k,int *rec[10],int *head,int *tail)
    {
        if (k == 0)
            return NULL;
        int *cur = (int *)malloc(k*sizeof(int));
        for (int i = 0; i<10; i++)
        {
            head[i] = tail[i] = 0;
        }
        int curSize = 0;
        for(int i = 0; i<n - k; i++)
        {
            int u = nums[i];
            rec[u][tail[u]++] = i;
        }
        for (int i = 0, last = 0; i<k; i++)
        {
            int u = nums[i + n - k];
            rec[u][tail[u]++] = i + n - k;
            for (int j = 9; j >= 0; j--)
            {
                if (head[j] != tail[j])
                {
                    cur[curSize++] = j;
                    int end = rec[j][head[j]];
                    while (last <= end)
                    {
                        int u = nums[last++];
                        head[u]++;
                    }
                    break;
                }
            }
        }
        return cur;
    }
    int* maxNumber(int* nums1, int nums1Size, int* nums2, int nums2Size, int k, int* returnSize) {
        int n = nums1Size>nums2Size ? nums1Size : nums2Size;
        int *ans=NULL,*rec[10], head[10], tail[10];
        for (int i = 0; i < 10; i++)
        {
            rec[i] = (int*)malloc(n*sizeof(int));
        }
    
        for (int k1 = 0; k1 <= k&&k1 <= nums1Size; k1++)
        {
            int k2 = k - k1;
            if (k2>nums2Size)
                continue;
            int *cur1 = calc(nums1, nums1Size, k1, rec, head, tail), *cur2 = calc(nums2, nums2Size, k2, rec, head, tail), *curans = (int*)malloc(k*sizeof(int)), flag = 1,flag1=1;
            
            for (int i = 0, j1 = 0, j2 = 0; i < k; i++)
            {
                
                if (j1 < k1&&j2 < k2)
                {
                    int f = 1;
                    for (int u1 = j1, u2 = j2; u1 < k1&&u2 < k2; u1++, u2++)
                    {
                        if (cur1[u1]>cur2[u2])
                        {
                            curans[i] = cur1[j1++];
                            f = 0;
                            break;
                        }
                        else if (cur1[u1] < cur2[u2])
                        {
                            curans[i] = cur2[j2++];
                            f = 0;
                            break;
                        }
                    }
                    if (f)
                    {
                        if (k1 - j1>k2 - j2)
                            curans[i] = cur2[j2++];
                        else
                            curans[i] = cur1[j1++];
                    }
                }
                else if (j1 < k1)
                {
                    curans[i] = cur1[j1++];
                }
                else
                {
                    curans[i] = cur2[j2++];
                }
                if (flag1&&ans!=NULL)
                {
                    if (curans[i] < ans[i])
                    {
                        flag = 0;
                        break;
                    }
                    else if (curans[i]>ans[i])
                    {
                        flag1 = 0;
                    }
                }
                
            }
            if (flag)
            {
                free(ans);
                ans = curans;
            }
            else
            {
                free(curans);
            }
        }
        *returnSize = k;
        return ans;
    }

ps：题主是不是unnc的啊？