c solution
\nint** findDifference(int* nums1, int nums1Size, int* nums2, int nums2Size, int* returnSize, int** returnColumnSizes){\n    /* range -1000 - 1000, 2001 totally
```\nint** findDifference(int* nums1, int nums1Size, int* nums2, int nums2Size, int* returnSize, int** returnColumnSizes){\n    /* range -1000 - 1000, 2001 totally */\n    int* hash = (int*)calloc(2001, sizeof(int));\n    int** ans = (int**)malloc(sizeof(int*) * 2);\n    ans[0] = (int*)calloc(nums1Size, sizeof(int));\n    ans[1] = (int*)calloc(nums2Size, sizeof(int));\n    \n    for(int i = 0; i < nums2Size; i++)\n        hash[nums2[i]+1000] = 1;\n    \n    for(int i = 0; i < nums1Size; i++)\n    {\n        if(hash[nums1[i]+1000]>0)/* means both num1 and num2 existed */\n            hash[nums1[i]+1000]++;\n        else /* only num1 has */\n            hash[nums1[i]+1000] = -1;\n    }\n    int* col = (int*)calloc(2, sizeof(int));\n    for(int i = -1000; i <= 1000; i++)\n    {\n        if(hash[i+1000] == -1)/* num1 */\n            ans[0][col[0]++] = i;\n        else if(hash[i+1000] == 1)/* num2 */\n            ans[1][col[1]++] = i;\n    }\n    \n    *returnSize = 2;\n    *returnColumnSizes = col;\n    return ans;\n}\n```
['C']