solution.cpp

#include <stdio.h>
#include <stdlib.h>
struct TreeNode
{
	int val;
	struct TreeNode *left;
	struct TreeNode *right;
};
static struct TreeNode *dfs(int low, int high, int *count)
{
	int i, j, k;
	if (low > high)
	{
		*count = 0;
		return NULL;
	}
	else if (low == high)
	{
		struct TreeNode *node = malloc(sizeof(*node));
		node->val = low;
		node->left = NULL;
		node->right = NULL;
		*count = 1;
		return node;
	}
	else
	{
		*count = 0;
		int capacity = 5;
		struct TreeNode *roots = malloc(capacity * sizeof(struct TreeNode));
		for (i = low; i <= high; i++)
		{
			int left_cnt, right_cnt;
			struct TreeNode *left_subs = dfs(low, i - 1, &left_cnt);
			struct TreeNode *right_subs = dfs(i + 1, high, &right_cnt);
			if (left_cnt == 0)
				left_cnt = 1;
			if (right_cnt == 0)
				right_cnt = 1;
			if (*count + (left_cnt * right_cnt) >= capacity)
			{
				capacity *= 2;
				capacity += left_cnt * right_cnt;
				roots = realloc(roots, capacity * sizeof(struct TreeNode));
			}
			for (j = 0; j < left_cnt; j++)
			{
				for (k = 0; k < right_cnt; k++)
				{
					roots[*count].val = i;
					roots[*count].left = left_subs == NULL ? NULL : &left_subs[j];
					roots[*count].right = right_subs == NULL ? NULL : &right_subs[k];
					(*count)++;
				}
			}
		}
		return roots;
	}
}
static struct TreeNode **generateTrees(int n, int *returnSize)
{
	int i, count = 0;
	struct TreeNode *roots = dfs(1, n, &count);
	struct TreeNode **results = malloc(count * sizeof(struct TreeNode *));
	for (i = 0; i < count; i++)
	{
		results[i] = &roots[i];
	}
	*returnSize = count;
	return results;
}
static void dump(struct TreeNode *node)
{
	printf("%d ", node->val);
	if (node->left != NULL)
	{
		dump(node->left);
	}
	else
	{
		printf("# ");
	}
	if (node->right != NULL)
	{
		dump(node->right);
	}
	else
	{
		printf("# ");
	}
}
int main(int argc, char **argv)
{
	if (argc != 2)
	{
		fprintf(stderr, "Usage: ./test n\n");
		exit(-1);
	}
	int i, count = 0;
	struct TreeNode **results = generateTrees(atoi(argv[1]), &count);
	for (i = 0; i < count; i++)
	{
		dump(results[i]);
		printf("\n");
	}
	return 0;
}