Official PYQ · 2023Q37TreesMCQ2 marks

GATE CS 2023 Q37 — Trees

Consider the $\text{C}$ function $\text{foo}$ and the binary tree shown.

typedef struct node {
    int val;
    struct node *left, *right;
} node;

int foo(node *p) {
    int retval;
    if (p == NULL)
        return 0;
    else {
        retval = p->val + foo(p->left) + foo(p->right);
        printf("%d ", retval);
        return retval;
    }
}

When $\textsf{foo}$ is called with a pointer to the root node of the given binary tree, what will it print?

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Answer: C

The function foo(p) performs a post-order traversal (Left $\rightarrow$ Right $\rightarrow$ Root) of the binary tree. For any node $p$ , it computes the sum of all node values in the subtree rooted at $p$ , prints this sum, and then returns it.

The binary tree structure is as follows:

Root node: $10$
Left child of $10$ : $5$ (with left child $3$ and right child $8$ )
Right child of $10$ : $11$ (with right child $13$ )

We trace the execution of foo post-order:

foo(3): A leaf node. Prints $3 + 0 + 0 = 3$ , returns $3$ .
foo(8): A leaf node. Prints $8 + 0 + 0 = 8$ , returns $8$ .
foo(5): Prints $5 + \text{foo}(3) + \text{foo}(8) = 5 + 3 + 8 = 16$ , returns $16$ .
foo(13): A leaf node. Prints $13 + 0 + 0 = 13$ , returns $13$ .
foo(11): Prints $11 + 0 + \text{foo}(13) = 11 + 13 = 24$ , returns $24$ .
foo(10): Prints $10 + \text{foo}(5) + \text{foo}(11) = 10 + 16 + 24 = 50$ , returns $50$ .

The printed sequence is: 3 8 16 13 24 50.

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Published 10 Oct 2026

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