An extended binary tree or 2-tree is a binary tree T which each node has either 0 or 2 node children. The nodes with 0 children are called external nodes. and the nodes with 2 children are called internal code. A 2-tree where the internal nodes are denoted by circles and the external nodes are denoted by square. In any 2-tree, the number NE of external nodes is 1 more than the number N1 of internal nodes; that is,
NE = N1 + 1;
Example: 2-tree, N1 = 6 and NE = N1 + 1 = 7
LE = 2+2+3+4+4+3+3 and L1 = 0+1+1+2+3+2 = 9
Observe That L1 + 2n = 9+2.6 = 9+12 = 21 = LE
Where n = 6 is the number of internal nodes. Formula LE = L1
+ 2n LE = 2+2+3+4+4+3+3 and L1 = 0+1+1+2+3+2 = 9
Observe That L1 + 2n = 9+2.6 = 9+12 = 21 = LE
Where n = 6 is the number of internal nodes. Formula LE = L1
is true for any 2-tree with n internal nodes.
Suppose T is a 2-tree with n external nodes, and suppose each of the external nodes is assigned a weight. The weighted path length P of the tree T is defined to be the sum of weighted path length ; i.e,
P = W1L1 + W2L2 +..............+ WnLn
Where Wi and Li denote, respectively, the weight and path length of an external node Ni
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