S4. Daily Commute
의견: 0
Toronto has \(N\) subway stations,
numbered from \(1\) to \(N\). You start at station \(1\), and every day, you need to reach
station \(N\) to get to school.
There are \(W\) one-way
walkways running amongst the stations, the \(i\)th of which allows you to
walk from station \(A_i\)
to a different station \(B_i\)
\((1 \le A_i, B_i \le N, A_i \not= B_i)\) in 1 minute. There may be
multiple walkways connecting any given pair of stations.
The subway line follows a certain route through the \(N\) stations, starting at station \(1\) and visiting each station once.
Initially, this route consists of stations \(S_1, S_2, ..., S_N\), in that order. \(S_1 = 1\), and \(S_{2}, \ldots, S_{N}\) is a permutation of
the integers \(2, \ldots, N\). Only one
subway train runs along this route per day, departing from station 1 at
6am in the morning and taking 1 minute to reach each subsequent station.
This means that, \(m\) minutes after
6am, the train will be at station \(S_{m+1}\) (or at station \(S_N\) if \(m \ge N-1\)).
Over a period of \(D\) days,
however, the subway line’s route will keep changing. At the start of the
\(i\)th day, the \(X_i\)th station and \(Y_i\)th station \((2 \le X_i, Y_i \le N, X_i \not= Y_i)\) in the route will be
swapped. Note that, after each such change, the route will still begin
at station \(1\) and will visit all
\(N\) stations once each. Changes will
carry over to subsequent days – the route will not automatically reset
itself back to \(S_1,\ldots,S_N\).
On each of these \(D\) days, you’d
like to determine how quickly you can get to school so you can begin
learning things. On the \(i\)th day, starting at 6am in
the morning (after the \(i\)th update to the subway
line’s route), you’ll begin your daily trip to station \(N\). Each minute, you may either ride the
subway to its next stop (if you’re currently at the same station as the
train and it hasn’t already completed its route), take a walkway from
your current station to another one, or wait at your current station.
Note that your trip begins at the same time as the train’s route,
meaning that you may choose to immediately ride it if you’d like to, and
that you may choose to leave and then get back on the train during your
trip.
\((1 \le A_i, B_i \le N, A_i \not= B_i)\)
\(m \ge N-1\)
\((2 \le X_i, Y_i \le N, X_i \not= Y_i)\)
\((1 \le i \le W)\)
\((1 \le i \le D)\)
Marks
The following table shows how the available 15 marks are
distributed.
| 2 marks | \(3 \le N \le 10\) | \(0 \le W \leq 10\) | \(1 \le D \le 10\) |
|---|---|---|---|
| 2 marks | \(3 \le N \leq 200\) | \(0 \le W \leq 200\) | \(1 \le D \le 200\) |
| 3 marks | \(3 \le N \leq 2000\) | \(0 \le W \leq 2000\) | \(1 \le D \le 2000\) |
| 8 marks | \(3 \le N \leq 200\,000\) | \(0 \le W \leq 200\,000\) | \(1 \le D \le 200\,000\) |
The first line contains three space-separated integers, \(N\), \(W\), and \(D\).
The next \(W\) lines each contain two
space-separated integers, \(A_i\) and
\(B_i\) \((1 \le i \le W)\).
The next line contains the \(N\)
space-separated integers, \(S_{1}, \ldots, S_{N}\), which form the initial permutation of stations.
The next \(D\) lines each contain two
space-separated integers, \(X_i\) and
\(Y_i\) \((1 \le i \le D)\).
The output is \(D\) lines, with one integer per line. The \(i\)th line is the minimum number
of minutes required to reach station \(N\) on the \(i\)th day (\(1 \le i \le D\)).
4 3 3
1 2
3 4
4 1
1 4 3 2
3 4
4 2
3 21
2
3At the start of the first day, the subway line’s route will be updated
to visit stations \([1, 4, 2, 3]\), in
that order. On that day, you should simply take the subway to station
\(4\), taking 1 minute.
On the second day, the route will become \([1, 3, 2, 4]\), and you should take the
subway to station \(3\) (taking 1
minute) and then walk to station \(4\)
(taking 1 more minute).
On the third day, the route will become \([1, 2, 3, 4]\). One choice of optimal trip
involves walking to station 2 (taking 1 minute), then boarding the train
there and taking it through station 3 and finally to station 4 (taking
another 2 minutes).
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S4. Daily Commute
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S4. Daily Commute