counting occurrences of word in binary search tree - c

Question

I'm working on creating a function word_count that counts the number of occurrences of the given word in a binary search. I'm having some trouble with how the logic would work, I'm stuck on the initial part. There's another function I created word_observe, that checks if a word is in the tree if it is not it adds it in and sets the count to one. If it is it increments count every time it comes across it. That could possibly be useful to understand the full program.
typedef struct tnode {
char *word;
int count;
struct tnode *left;
struct tnode *right;
} tnode;
tnode *word_observe(char *word, tnode *node) {
if (node != NULL) {
if (strcmp(node->word, word) == 0) {
node->count++;
return node;
} else if (strcmp(node->word, word) < 0) {
node->left = word_observe(word, node->left);
} else {
node->right = word_observe(word, node->right);
}
} else {
tnode *newnode = (tnode*)malloc(sizeof(tnode));
newnode->word = strdup(word);
newnode->count = 1;
newnode->left = NULL;
newnode->right = NULL;
node = newnode;
}
return node;
}
int word_count(char *word, tnode *node) {
if (node != NULL) {
if (strcmp(node->word, word) == 0) {
return node->count;
} else if (strcmp(word, node->word) < 0) {
word_count(word, node->left);
} else {
word_count(word, node->right);
}
}
return -1;
}
int main(void) {
tnode *counts = NULL;
counts = word_observe("dog", counts);
counts = word_observe("dog", counts);
counts = word_observe("apple", counts);
counts = word_observe("hello", counts);
counts = word_observe("pineapple", counts);
counts = word_observe("pineapple", counts);
counts = word_observe("pineapple", counts);
counts = word_observe("zebra", counts);
counts = word_observe("zebra", counts);
counts = word_observe("zebra", counts);
counts = word_observe("zebra", counts);
printf("apple: %d\n", word_count("apple", counts));
printf("dog: %d\n", word_count("dog", counts));
printf("pineapple: %d\n", word_count("pineapple", counts));
printf("zebra: %d\n", word_count("zebra", counts));
return 0;
}

Answer 1

You're kind of close. Your word_count function isn't searching correctly, which is puzzling since you are doing this correctly in word_observe. You need to search down the left side for < words and down the right side for > words. Since you're using recursion, you need to return those calls directly. When the word is found, simply return node->count, what you're doing invokes undefined behavior since count isn't initialized. Finally, you must return a value to indicate if the word isn't found.
int word_count(char *word, tnode *node) {
if (node != NULL) {
if (strcmp(node->word, word) == 0) {
// found the word, return its count. This value will
// ride the `return`s up the stack until it's returned back to main
return node->count;
} else if (strcmp(node->word, word) < 0) {
// < word, take the left path
return word_count(word, node->left);
} else {
// > word, take the right path
return word_count(word, node->right);
}
}
// couldn't find the word, return -1
return -1;
}
Working demo