Problem #450
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Tags:
c-1
puzzle
combinatorics
Ann and Bob found three large jars full of beads. The first jar contained a mixture of red
and blue
beads. All of the beads in the
second jar were yellow
and all of the beads in the third jar were green
. Ann and Bob decided to play a game with the beads. One of them
would think of a number (N
) and then each of them would take N
beads from the jar containing red
and blue
beads. Each of them would then
arrange their beads in a straight line.
Ann and Bob then decided to create a new line of N
beads based on the two lines that they had created. For each of the positions 1
to N
in
the two lines of beads, they compare the two beads at this position. If the two beads were the same colour they put a yellow bead into the new
line. If the two beads were different colours they put a green bead into the new line. Eventually they had a new line of N
beads, consisting
of yellow and green beads only.
Ann and Bob realised that they could have arranged their lines of red
and blue
beads in many different ways. This means that there are many
possibilities for the new line of yellow
and green
beads. Ann and Bob wondered whether it was possible to work out just how many different
lines of yellow
and green
beads could be created from the two sets of N
red and blue beads. They decided to look at the following simple
example where each of them chose just 4
beads. Ann chose 1
red bead and 3
blue beads. Bob chose 2
red beads and 2
blue beads. Ann can
arrange her 4
beads in 4
different ways. Bob can arrange his 4
beads in 6
different ways. Hence there are 24
different ways of
combining the two sets of beads. These are shown in the table below, together with the corresponding yellow and green line
R B B B R R B B Y G Y Y
R B B B R B R B Y Y G Y
R B B B R B B R Y Y Y G
R B B B B R R B G G G Y
R B B B B R B R G G Y G
R B B B B B R R G Y G G
B R B B R R B B G Y Y Y
B R B B R B R B G G G Y
B R B B R B B R G G Y G
B R B B B R R B Y Y G Y
B R B B B R B R Y Y Y G
B R B B B B R R Y G G G
B B R B R R B B G G G Y
B B R B R B R B G Y Y Y
B B R B R B B R G Y G G
B B R B B R R B Y G Y Y
B B R B B R B R Y G G G
B B R B B B R R Y Y Y G
B B B R R R B B G G Y G
B B B R R B R B G Y G G
B B B R R B B R G Y Y Y
B B B R B R R B Y G G G
B B B R B R B R Y G Y Y
B B B R B B R R Y Y G Y
Although the 24
combinations of red and blue lines are all different, the same is not true of the yellow and green lines. There are only 8
distinct combinations.
You will be given the number of red
and blue
beads (Ra
and Ba
) chosen by Ann, as well as the number of red
and blue
beads (Rb
and Bb
)
chosen by Bob
. It is guaranteed that Ra + Ba = Rb + Bb = N
. You are to find the total number of distinct lines of yellow
and green
beads
which can be created by following the rules of the game. As this number can be very large you are asked to give the answer modulo 1000000007 (10^9 +7)
.
You can assume that the value of N
will always be smaller than one million.
Input and Answer:
The first line of the problem will be a single integer T
denoting the number of test cases.
Each test case has a single line of data consisting of 4
integers, Ra
, Ba
, Rb
andBb
. For each test case give the number of distinct
yellow
and green
lines that can be made; giving the answer modulo 1000000007
. Combine all answers into a single string, separated by
single spaces.
Example:
input:
3
1 3 2 2
1 8 6 3
32 3 6 29
answer:
8 162 77663157