A tree with n vertices is called graceful, if its vertices can be labelled with integers 1, , ..., 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?
absolute value is only when a value there is no difference with sign bit.
where u got that concept "cannot take value greater than no. of vertex"
n vertices is called graceful, if its vertices can be labelled with integers 1, , ..., n from here.
Alternative Solution
D is ans