Is a Binary Tree Contained Within Another Binary Tree - C - c

Question

So I just had an interview that I'm confident I screwed up royally. I had a bunch of questions thrown at me and didn't have enough time to answer the last one.
After getting all beginning questions correct, I was asked to write a function that would determine whether a binary tree b is contained within another binary tree a. I coded the question prior to that correctly, in which he asked me to write a function to determine whether two trees are equal:
int sameTree(struct node *a, struct node *b){
//both empty = TRUE
if(a == NULL && b == NULL)
return TRUE;
//both not empty, compare them
else if(a != NULL && b != NULL){
return(
a->data == b->data &&
sameTree(a->left, b->left) &&
sameTree(a->right, b->right)
);
}
//one empty, one not = FALSE
else
return FALSE;
}
Ugh. Just for clearing my conscience, again how would you determine whether tree b is inside tree a?
Thanks for any help guys.

Answer 1

int in(struct node* outer, struct node* inner){
if(inner == null){
return true; // say every tree contains the empty tree
} else if(outer == null){
return false;
} else if(same(outer, inner)){
return true;
} else return in(outer->left, inner) || in(outer->right, inner);
}
We must not use the OP's sameTree but rather this function:
int same(struct node* outer, struct node* inner){
return !inner || outer && outer->data == inner->data && same(outer->left, inner->left) && same(outer->right, inner->right);
}
Or, more verbosely,
int same(struct node* outer, struct node* inner){
if(inner == null){
return true;
} else if(outer == null){
return false;
} else if(outer->data == inner->data){
return same(outer->left, inner->left) && same(outer->right, inner->right);
} else return false;
}

Answer 2

This assumes you want the same tree with the same structure, contains in a:
For one, if b is null and a isn't, a contains b (you should check that in your last else).
Second, these aren't binary search trees (unsorted), so to check if b is inside a you should also traverse a (assuming you rename the function):
int containsTree(struct node *a, struct node *b){
//both empty = TRUE
if(a == NULL && b == NULL)
return TRUE;
//both not empty, compare them
else if(a != NULL && b != NULL){
return(
// sameTree should be changed to allow nulls, as below
sameTree(a, b)
// check recursively
|| containsTree(a->left, b)
|| containsTree(a->right, b)
);
//one empty, one not = FALSE
else
return B == NULL;

Answer 3

To check if tree A is contained as-is in tree B, find the node C in B such that C.data == A.data. If there is no such node, A is not contained in B. If C exists, check if A and C are equal using a modified sameTree function - one that ignores mismatches between null children of A and non-null children of C (return true if A.left/right is null).
Thanks #Kobi for the correction.