[USACO11NOV] Above the Median G

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. 给出一串数字，问中位数大于等于X的连续子串有几个。（这里如果有偶数个数，定义为偏大的那一个而非中间取平均）

\* Line 1: Two space-separated integers: N and X. \* Lines 2..N+1: Line i+1 contains the single integer H\_i.

\* 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.

4 6 
10 
5 
6 
2 

7 

FJ's four cows have heights 10, 5, 6, 2. We want to know how many contiguous subsequences have median at least 6. 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}.