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Question

A tree with n vertices is called graceful, if its vertices can be labelled with integers 1, 2, ...,n such that the absolute value of the difference of the labels of adjacent vertices are all different. Which of the following trees are graceful?

a.

(a) and (b)

b.

(b) and (c)

c.

(a) and (c)

d.

(a), (b) and (c)

Answer: (d).(a), (b) and (c)

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Q. A tree with n vertices is called graceful, if its vertices can be labelled with integers 1, 2, ...,n such that the absolute value of the difference of the labels of adjacent...

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