USACO 2011 November Contest, Gold Division
Problem 1. Above the Median
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Problem 1: Above the Median [Brian Dean]
Farmer John has lined up his N (1 <= N <= 100,000) cows in a row to measure
their heights; cow i has height H_i (1 <= H_i <= 1,000,000,000)
nanometers--FJ believes in precise measurements! He wants to take a picture
of some contiguous subsequence of the cows to submit to a bovine
photography contest at the county fair.
The fair has a very strange rule about all submitted photos: a photograph
is only valid to submit if it depicts a group of cows whose median height
is at least a certain threshold X (1 <= X <= 1,000,000,000).
For purposes of this problem, we define the median of an array A[0...K] to
be A[ceiling(K/2)] after A is sorted, where ceiling(K/2) gives K/2 rounded
up to the nearest integer (or K/2 itself, it K/2 is an integer to begin
with). For example the median of {7, 3, 2, 6} is 6, and the median of {5,
4, 8} is 5.
Please help FJ count the number of different contiguous subsequences of his
cows that he could potentially submit to the photography contest.
PROBLEM NAME: median
INPUT FORMAT:
* Line 1: Two space-separated integers: N and X.
* Lines 2..N+1: Line i+1 contains the single integer H_i.
SAMPLE INPUT (file median.in):
4 6
10
5
6
2
INPUT DETAILS:
FJ's four cows have heights 10, 5, 6, 2. We want to know how many
contiguous subsequences have median at least 6.
OUTPUT FORMAT:
* Line 1: The number of subsequences of FJ's cows that have median at
least X. Note this may not fit into a 32-bit integer.
SAMPLE OUTPUT (file median.out):
7
OUTPUT DETAILS:
There are 10 possible contiguous subsequences to consider. Of these, only 7
have median at least 6. They are {10}, {6}, {10, 5}, {5, 6}, {6, 2}, {10,
5, 6}, {10, 5, 6, 2}.
Contest has ended. No further submissions allowed.