Codechef Q - Why am I getting a “Wrong Answer”

Question

Sorry for the short title, SO won't let me post anything else.

I've written the following solution to the problem PHYSICS ( http://www.codechef.com/problems/PHYSICS ), it passes the simple test case provided but on submitting its results in WA(wrong answer) for all test cases.

import numbers

T = input()

for t in xrange(T):

N, F = [int(i) for i in raw_input().split()]
heights = [(long(i), False) for i in raw_input().split()]

heights.sort()
heights.reverse()

ways = 0
for i, h in enumerate(heights):
    height = h[0]
    used = h[1]
    if used:
        continue
    j = 0
    while True:
        force = F ** j
        if force > height:
            break
        bounce = height / force
        if isinstance(bounce, numbers.Integral):
            try:
                if len(heights) > i:
                    index = heights.index((bounce, False), i + 1)
                    if index != i:
                        heights[index] = (bounce, True)
                        ways += 1
                        break
            except ValueError:
                pass
            finally:
                j += 1
print ways

This is what I'm doing in my solution :

• for all the children in classroom heights list stores tuple(height, used) where height is the height of a child and boolean used indicates if child has been already used in forming a pair or not.
• the while loop checks if there's child whose height is equal to for all possible bounces

Help me spot the cases where this solution can fail, and the fix.

Answer 1

I think you got the problem a bit wrong. You may use a child in more than one pair, the only special case is when two children have the same height. As a result you overcomplicate the solution a bit. Are you printing correct answer to example case 2? It seems that you will only count one pair with 4 while in fact it takes part in two pairs.