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Choose the correct alternatives (more than one may be correct) and write the corresponding letters only:

A $2-3$ tree is such that

1. All internal nodes have either $2$ or $3$ children
2. All paths from root to the leaves have the same length.

The number of internal nodes of a $2-3$ tree having $9$ leaves could be

1. $4$
2. $5$
3. $6$
4. $7$

edited | 727 views

Answer (a) 4, (d) 7

$4 \rightarrow$ When each leaf has $3$ childs. So $9/3 = 3$ Internal nodes, Then one internal node those internal nodes.

$7 \rightarrow$ When each leaf has $2$ childs & one leaf out of $4$ get $3$ childs. Ex $\rightarrow 8/4 = 2$ child per internal node. Then one of that internal node get extra third child. Then $2$ internal nodes to connect these $4$. Then $1$ internal node to connect this $2$. So $4+2+1 = 7$.

No other way is possible.

answered by Veteran (49.5k points)
edited by
We are also considering root as an internal node right?
is there any specific procedure for this ques....?????????

6 also possible ans

@srestha plz check bcoz it not satisfy this which is given in question  All paths from root to the leaves have the same length.

yes thanks
Am getting only 4 and 7 4-> complete 3 ary-tree 7-> almost complete binary tree ...almost in the sense one of penultimate level node has 3 children
answered by Veteran (14.3k points)
Same here.

In 2-3 Tree for 9 leaves, internal nodes can be 4 or 7

answered by Junior (941 points)
In the second diagram you have made 10 leaves . Plz see it .Question is asking about 9 leaves only.
@ashwina, yes you are correct, that was a mistake. please assume 9 leaf nodes in the 2nd tree.
+1 vote

Ans should be 4 and 7

answered by Boss (7.9k points)