Usaco Jan09 Gold

Part of USACO Jan09

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GOLD PROBLEMS
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Three problems numbered 1 through 3
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Problem 1: Earthquake Damage [Hal Burch, 2004]

Wisconsin has had an earthquake that has struck Farmer John's farm!
The earthquake has damaged some of the pastures so that they are
unpassable. Remarkably, none of the cowpaths was damaged.

As usual, the farm is modeled as a set of P (1 <= P <= 30,000)
pastures conveniently numbered 1..P which are connected by a set
of C (1 <= C <= 100,000) non-directional cowpaths conveniently
numbered 1..C. Cowpath i connects pastures a_i and b_i (1 <= a_i
<= P; 1 <= b_i <= P). Cowpaths might connect a_i to itself or perhaps
might connect two pastures more than once.  The barn is located in
pasture 1.

A total of N (1 <= N <= P) cows (in different pastures) sequentially
contact Farmer John via moobile phone with an integer message
report_j (2 <= report_j <= P) that indicates that pasture report_j
is undamaged but that the calling cow is unable to return to the
barn from pasture report_j because she could not find a path that
does not go through damaged pastures.

After all the cows report in, determine the minimum number of
pastures (including ones that are uncrossable) from which it is not

Note: Feedback on some of the test data will be provided on the
first 50 submissions

PROBLEM NAME: damage

INPUT FORMAT:

* Line 1: Three space-separated integers: P, C, and N

* Lines 2..C+1: Line i+1 describes cowpath i with two integers: a_i
and b_i

* Lines C+2..C+N+1: Line C+1+j contains a single integer: report_j

SAMPLE INPUT (file damage.in):

4 3 1
1 2
2 3
3 4
3

OUTPUT FORMAT:

* Line 1: A single integer that is the minimum count of pastures from
which a cow can not return to the barn (including the damaged
pastures themselves)

SAMPLE OUTPUT (file damage.out):

3

OUTPUT DETAILS:

Pasture 2 is damaged, resulting in cows in pastures 2, 3, 4 not being able to

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Problem 2: The Baric Bovine [Jeffrey Wang, 2007]

Following up on a journal article about increasing milk production,
Bessie has become the Baric Bovine by studying atmospheric pressure
in order to curry favor with Farmer John.

She takes N (1 <= N <= 100) measurements conveniently named M_1
through M_N during the day (1 <= M_i <= 1,000,000); these measurements
are numbered in the order in which Bessie observed them.

In order to characterize the day's atmospheric pressure readings,
she is interested in finding a subset of the measurements (given
by the K (1 <= K <= N) indices s_j where 1 <= s_1 < s_2 < ... < s_K
<= N) that accurately reflects the entire set, i.e., limits the
error as described below.

In any subset of measurements, an error is incurred for each
measurement (1) before the first member of the subset, (2) between
two consecutive measurements in the subset, and (3) after the last
member of the subset. The total error value for a given set of s_j
values is the sum of each of the individual errors.

Specifically, for all measurements whose index i is not one of the
s_j values:

* if i is less than s_1, then the sample error is:
2 * | M_i - M_(s_1) |

* if i is between s_j and s_(j+1), then the sample error is
| 2 * M_i - Sum(s_j, s_(j+1)) |
where Sum(x, y) = M_x + M_y;

* if i is greater than s_K, then the sample error is
2 * | M_i - M_(s_K) |

Given a maximum error value E (1 <= E <= 1,000,000), determine the
size of the smallest subset of measurements that produces an error
of at most E.

PROBLEM NAME: baric

INPUT FORMAT:

* Line 1: Two space-separated integers: N and E

* Lines 2..N+1: Line i+1 contains a single integer: M_i

SAMPLE INPUT (file baric.in):

4 20
10
3
20
40

INPUT DETAILS:

Bessie takes four measurements; the maximum error is 20. The
measurements are, in sequence: 10, 3, 20, and 40.

OUTPUT FORMAT:

* Line 1: Two space-separated integers: the size of the smallest
subset of measurements that produces an error of at most E and
the least possible error for the subset of that size.

SAMPLE OUTPUT (file baric.out):

2 17

OUTPUT DETAILS:

Choosing the second and fourth measurements is the best option,
giving an error of 17. The first term's error is 2*|10-3| = 14; the
third term's error is |2*20 - (3+40)| = 3.

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Problem 3: Safe Travel [Long Fan, 2008]

Gremlins have infested the farm. These nasty, ugly fairy-like
creatures thwart the cows as each one walks from the barn (conveniently
located at pasture_1) to the other fields, with cow_i traveling to
from pasture_1 to pasture_i. Each gremlin is personalized and knows
the quickest path that cow_i normally takes to pasture_i. Gremlin_i
waits for cow_i in the middle of the final cowpath of the quickest
route to pasture_i, hoping to harass cow_i.

Each of the cows, of course, wishes not to be harassed and thus
chooses an at least slightly  different route from pasture_1 (the
barn) to pasture_i.

Compute the best time to traverse each of these new not-quite-quickest
routes that enable each cow_i that avoid gremlin_i who is located
on the final cowpath of the quickest route from pasture_1 to
pasture_i.

As usual, the M (2 <= M <= 200,000) cowpaths conveniently numbered
1..M are bidirectional and enable travel to all N (3 <= N <= 100,000)
pastures conveniently numbered 1..N. Cowpath i connects pastures
a_i (1 <= a_i <= N) and b_i (1 <= b_i <= N) and requires t_i (1 <=
t_i <= 1,000) time to traverse. No two cowpaths connect the same
two pastures, and no path connects a pasture to itself (a_i != b_i).
Best of all, the shortest path regularly taken by cow_i from pasture_1
to pasture_i is unique in all the test data supplied to your program.

By way of example, consider these pastures, cowpaths, and [times]:

1--[2]--2-------+
|       |       |
[2]     [1]     [3]
|       |       |
+-------3--[4]--4

TRAVEL     BEST ROUTE   BEST TIME   LAST PATH
p_1 to p_2       1->2          2         1->2
p_1 to p_3       1->3          2         1->3
p_1 to p_4      1->2->4        5         2->4

When gremlins are present:

TRAVEL     BEST ROUTE   BEST TIME    AVOID
p_1 to p_2     1->3->2         3         1->2
p_1 to p_3     1->2->3         3         1->3
p_1 to p_4     1->3->4         6         2->4

For 20% of the test data, N <= 200.

For 50% of the test data, N <= 3000.

TIME LIMIT: 3 Seconds

MEMORY LIMIT: 64 MB

PROBLEM NAME: travel

INPUT FORMAT:

* Line 1: Two space-separated integers: N and M

* Lines 2..M+1: Three space-separated integers: a_i, b_i, and t_i

SAMPLE INPUT (file travel.in):

4 5
1 2 2
1 3 2
3 4 4
3 2 1
2 4 3

INPUT DETAILS:

As in the text example.

OUTPUT FORMAT:

* Lines 1..N-1: Line i contains the smallest time required to travel
from pasture_1 to pasture_i+1 while avoiding the final cowpath
of the shortest path from pasture_1 to pasture_i+1. If no such
path exists from pasture_1 to pasture_i+1, output -1 alone on
the line.

SAMPLE OUTPUT (file travel.out):

3
3
6

OUTPUT DETAILS:

As in the text example.

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page revision: 0, last edited: 06 Jun 2009 21:32