Questions

Full binary tree loses its nature when operations of insertions and deletions are done. For incomplete binary trees, extra storage is required and overhead of NULL node checking takes place. So complete binary tree is the better one since the property of complete binary tree is maintained even after operations like additions and deletions are done on it.

9 P in SS  is a short form for 9 Planets i  Solar System.

There are many more of this kind. Some of them are:

1. 7 C in a R        -    7 Colours in a Rainbow

2.  90 D in a R A   -    90 Degrees in a Right Angle

3.  52 W in a Y     -    52 Weeks in a Year

4.  5 C in an OF

5.  12 S of the Z

The submerged portion of the ice on melting shrinks a little in volume. so the level of water goes down a little.But this is just made up by the water added by the melting of upper portion. Addition is equal to the Shrinkage. Hence level is unchanged.

Yes, footsteps are what we take more, the more we leave behind.