solve.c

#include <stdio.h>
#include <stdbool.h>
#include <stdlib.h>

struct TreeNode {
	int val;
	struct TreeNode *left;
	struct TreeNode *right;
};
bool hasPathSum(struct TreeNode *root, int sum) {
	if (root == NULL)
		return false;
	if (root->left == NULL && root->right == NULL)
		return root->val == sum;
	if (!root->left || !hasPathSum(root->left, sum - root->val)) {
		return hasPathSum(root->right, sum - root->val);
	}
	return true;
}

struct TreeNode *mk_node(int val)
{
	struct TreeNode *p = malloc(sizeof(*p));
	p->val = val;
	p->left = p->right = NULL;
	return p;
}
void mk_child(struct TreeNode *root, struct TreeNode *left, struct TreeNode *right)
{
	root->left = left;
	root->right = right;
}
int main(int argc, char **argv)
{
	struct TreeNode *root = mk_node(5);
	mk_child(root, mk_node(4), mk_node(8));
	struct TreeNode *left = root->left;
	struct TreeNode *right = root->right;
	mk_child(left, mk_node(11), NULL);
	mk_child(left->left, mk_node(7), mk_node(2));
	mk_child(right, mk_node(13), mk_node(4));
	mk_child(right->right, NULL, mk_node(1));
	printf("%d\n", hasPathSum(root, 22));
	printf("%d\n", hasPathSum(root, 26));
	printf("%d\n", hasPathSum(root, 18));
	printf("%d\n", hasPathSum(root, 27));
	printf("%d\n", hasPathSum(root, 37));
	printf("%d\n", hasPathSum(root, 100));
	printf("%d\n", hasPathSum(root, 0));
	return 0;
}