题目：

题解：

int** levelOrderBottom(struct TreeNode* root, int* returnSize, int** returnColumnSizes) {
    int** levelOrder = malloc(sizeof(int*) * 2001);
    *returnColumnSizes = malloc(sizeof(int) * 2001);
    *returnSize = 0;
    if (!root) {
        return levelOrder;
    }
    struct TreeNode** q = malloc(sizeof(struct TreeNode*) * 2001);
    int left = 0, right = 0;
    q[right++] = root;
    while (left < right) {
        int len = right - left;
        int* level = malloc(sizeof(int) * len);
        (*returnColumnSizes)[*returnSize] = len;
        for (int i = 0; i < len; ++i) {
            struct TreeNode* node = q[left++];
            level[i] = node->val;
            if (node->left != NULL) {
                q[right++] = node->left;
            }
            if (node->right != NULL) {
                q[right++] = node->right;
            }
        }
        levelOrder[(*returnSize)++] = level;
    }
    for (int i = 0; 2 * i < *returnSize; ++i) {
        int* tmp1 = levelOrder[i];
        levelOrder[i] = levelOrder[(*returnSize) - i - 1];
        levelOrder[(*returnSize) - i - 1] = tmp1;
        int tmp2 = (*returnColumnSizes)[i];
        (*returnColumnSizes)[i] = (*returnColumnSizes)[(*returnSize) - i - 1];
        (*returnColumnSizes)[(*returnSize) - i - 1] = tmp2;
    }
    return levelOrder;
}