S1. Hat Circle
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At a recent social gathering, \(N\)
people sit around a circular table, where \(N\) is even. The seats are numbered
clockwise from \(1\) to \(N\). Each person is wearing a hat with a
number on it. Specifically, the person at seat \(i\) is wearing a hat with the number \(H_i\) on it.
Each person looks at the person who is directly across (diametrically
opposite) them in the circle.
Determine the number of people who see someone with a hat with the
same number as their own.
The first line of input will consist of one even positive integer
\(N\), representing the number of
people at the social gathering.
The next \(N\) lines each contain a
single non-negative integer \(H_i\),
representing the hat number of person \(i\).
Output a single integer representing the number of people who see
their hat number on the person directly across from them.
| 서브태스크 | 점수 | 설명 |
|---|---|---|
1 | 13점 | Very small number of people; only two hat numbers — \(N \le 4\) — \(H_i \leq 1\) |
2 | 6점 | Only one hat number — \(N \le 100\) — \(H_i = 1\) |
3 | 13점 | People in even numbered seats have hat number 1; people in odd numbered seats have hat number 0 — \(N \le 100\) — \(H_i \leq 1\) |
4 | 34점 | Medium number of people — \(N \le 2\,000\) — \(H_i \leq 4\,000\) |
5 | 34점 | Large number of people and hat numbers — \(N \le 1\,000\,000\) — \(H_i \le 2\,000\,000\) |
4
0
1
0
14The four seats around the table are shown below. Hat numbers are
shown inside each seat and seat numbers are shown beside each seat.
Notice that every person sees their hat number. The people in seats
\(1\) and \(3\) both see hat number \(0\), and the people in seats \(2\) and \(4\) both see hat number \(1\).
4
1
0
0
10The four seats around the table are shown below. Hat numbers are
shown inside each seat and seat numbers are shown beside each seat.
Notice that no person sees their hat number. The people in seats \(1\) and \(4\) both see hat number \(0\), and the people in seats \(2\) and \(3\) both see hat number \(1\).
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S1. Hat Circle
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S1. Hat Circle