Usaco Nov07 Silver

Part of USACO Nov07

                           SILVER PROBLEMS
                  Three problems numbered 6 through 8

Problem 6: Cow Hurdles [Neal Wu, 2007]

Farmer John wants the cows to prepare for the county jumping
competition, so Bessie and the gang are practicing jumping over
hurdles. They are getting tired, though, so they want to be able
to use as little energy as possible to jump over the hurdles.

Obviously, it is not very difficult for a cow to jump over several
very short hurdles, but one tall hurdle can be very stressful. Thus,
the cows are only concerned about the height of the tallest hurdle
they have to jump over.

The cows' practice room has N (1 <= N <= 300) stations, conveniently
labeled 1..N. A set of M (1 <= M <= 25,000) one-way paths connects
pairs of stations; the paths are also conveniently labeled 1..M.
Path i travels from station S_i to station E_i and contains exactly
one hurdle of height H_i (1 <= H_i <= 1,000,000). Cows must jump
hurdles in any path they traverse.

The cows have T (1 <= T <= 40,000) tasks to complete. Task i comprises
two distinct numbers, A_i and B_i (1 <= A_i <= N; 1 <= B_i <= N),
which connote that a cow has to travel from station A_i to station
B_i (by traversing over one or more paths over some route). The
cows want to take a path the minimizes the height of the tallest
hurdle they jump over when traveling from A_i to B_i. Your job is to
write a program that determines the path whose tallest hurdle is
smallest and report that height.



* Line 1: Three space-separated integers: N, M, and T

* Lines 2..M+1: Line i+1 contains three space-separated integers: S_i,
        E_i, and H_i

* Lines M+2..M+T+1: Line i+M+1 contains two space-separated integers
        that describe task i: A_i and B_i


5 6 3
1 2 12
3 2 8
1 3 5
2 5 3
3 4 4
2 4 8
3 4
1 2
5 1


* Lines 1..T: Line i contains the result for task i and tells the
        smallest possible maximum height necessary to travel between
        the stations. Output -1 if it is impossible to travel between
        the two stations.

SAMPLE OUTPUT (file hurdles.out):



Query #1: The best way is to simply travel on the path from station 3 to
station 4.
Query #2: There is a path from station 1 to station 2, but a better way
would be to travel from station 1 to station 3 and then to station 2.
Query #3: There are no paths that start at station 5, so it is clear that
there is no way to reach station 1 from station 5.


Problem 7: Milking Time [Jeffrey Wang, 2007]

Bessie is such a hard-working cow. In fact, she is so focused on
maximizing her productivity that she decides to schedule her next
N (1 <= N <= 1,000,000) hours (conveniently labeled 0..N-1) so that
she produces as much milk as possible.

Farmer John has a list of M (1 <= M <= 1,000) possibly overlapping
intervals in which he is available for milking. Each interval i has
a starting hour (0 <= starting_hour_i < N), an ending hour
(starting_hour_i < ending_hour_i <= N), and a corresponding efficiency
(1 <= efficiency_i <= 1,000,000) which indicates how many gallons
of milk that he can get out of Bessie in that interval. Farmer John
starts and stops milking at the beginning of the starting hour and
ending hour, respectively. When being milked, Bessie must be milked
through an entire interval.

Even Bessie has her limitations, though. After being milked during
any interval, she must rest R (1 <= R <= N) hours before she can
start milking again. Given Farmer Johns list of intervals, determine
the maximum amount of milk that Bessie can produce in the N hours.

PROBLEM NAME: milkprod


* Line 1: Three space-separated integers: N, M, and R

* Lines 2..M+1: Line i+1 describes FJ's ith milking interval with
        three space-separated integers: starting_hour_i,
        ending_hour_i, and efficiency_i


12 4 2
1 2 8
10 12 19
3 6 24
7 10 31


Bessie wants to schedule the next 12 hours; Farmer John has four
intervals in which he can milk her; Bessie must rest 2 hours after
every milking. The first interval lasts from hour 1 to hour 2, the
second from hour 10 to hour 12, the third from hour 3 to hour 6,
and the fourth from hour 7 to hour 10. Farmer John can get 8, 19,
24, and 31 gallons of milk, respectively, from Bessie in those


* Line 1: The maximum number of gallons of milk that Bessie can
        product in the N hours

SAMPLE OUTPUT (file milkprod.out):



If Bessie uses the first interval, she cannot use the third because
she needs 2 hours of rest. If she uses the second, she cannot use
the fourth.  Lastly, if she uses the third, she cannot use the
fourth. The best situation is choosing the second and third intervals,
producing 43 gallons of milk.


Problem 8: Best Cow Line [Christos Tzamos, 2007]

FJ is about to take his N (1 <= N <= 2,000) cows to the annual
"Farmer of the Year" competition. In this contest every farmer
arranges his cows in a line and herds them past the judges.

The contest organizers adopted a new registration scheme this year:
simply register the initial letter of every cow in the order they
will appear (i.e., If FJ takes Bessie, Sylvia, and Dora in that
order he just registers BSD). After the registration phase ends,
every group is judged in increasing lexicographic order according
to the string of the initials of the cows' names.

FJ is very busy this year and has to hurry back to his farm, so he
wants to be judged as early as possible. He decides to rearrange
his cows, who have already lined up, before registering them.

FJ marks a location for a new line of the competing cows. He then
proceeds to marshal the cows from the old line to the new one by
repeatedly sending either the first or last cow in the (remainder
of the) original line to the end of the new line. When he's finished,
FJ takes his cows for registration in this new order.

Given the initial order of his cows, determine the least lexicographic
string of initials he can make this way.



* Line 1: A single integer: N

* Lines 2..N+1: Line i+1 contains a single initial ('A'..'Z') of the
        cow in the ith position in the original line




FJ has 6 cows in this order: ACDBCB


The least lexicographic string he can make. Every line (except perhaps
the last one) contains the initials of 80 cows ('A'..'Z') in the new

SAMPLE OUTPUT (file bcl.out):



  Step   Original     New
   #1     ACDBCB
   #2      CDBCB     A
   #3      CDBC      AB
   #4      CDB       ABC
   #5      CD        ABCB
   #6       D        ABCBC
   #7                ABCBCD

Unless otherwise stated, the content of this page is licensed under Creative Commons Attribution-ShareAlike 3.0 License