Algorithms

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Algorithms
Mid-term Exam
April 19, 1999
1 Define the following terms:
1) Randomized algorithm
(3%)
2) Las Vegas algorithm
(3%)
3) Monte Carlo algorithm
(3%)
4) Õ(g(n))
(6%)
Sector 1.4.2 Randomized Algorithms. Page 53~54
2 T(n) ≤ 2T (n/2) + c n log n
Prove: T(n) = O(n(log n)2)
(10%)
Sector 3.1 Solving Recurrence Relations Page 128~130
3. The closest-pair problem is to find the two points that are
closest together among a set of points in the plane. Informally
describe a divide-and-conquer algorithm to solve this problem.
The time complexity of your algorithm may satisfy the
recurrence relation in problem 2.
(15%)
4. Sketch the process of a greedy algorithm in solving the job
sequencing problem below.
(p1, p2, p3, p4, p5, p6, p7) = (3, 5, 20, 18, 1, 6, 30)
(d1, d2, d3, d4, d5, d6, d7) = (1, 3, 4, 2, 2, 1, 2)
(10%)
Sector 4.4 Job Sequencing with deadlines Page 206~212
5. Here is a resource allocation problem:
3 projects, 3 units of resource,
N( i, j ) = profit resulting from allocating j units of resource
to project i.
N( 1, 1) = 1, N( 1, 2) = 2, N( 1, 3) = 3
N( 2, 1) = 2, N( 2, 2) = 2, N( 2, 3) = 3
N( 3, 1) = 2, N( 3, 2) = 3, N( 3, 3) = 3
1) Represent the problem as a multistage graph.
(10%)
1
2) Write the recurrence relation for the multistage graph
problem and solve the problem in part 1) step by step. (10%)
Section 5.2 Multistage graphs. Page 257~261
2
6. Show how you use set approach dynamic programming to solve
the following 0/1 knapsack problem step by step and give your
answer to the problem.
m = 20
(u1, u2, u3, u4) = (10, 15, 6, 9)
(p1, p2, p3, p4) = ( 2, 5, 8, 1)
(10%)
Sector 5.7 0/1-Knapsack Page 287~294
7. Let A and B be matrices of dimension mxn and nxp
respectively. The product C = AxB, an mxp matrix, can be
computed using mnp multiplications. Let M1xM2x…xMr be a
chain of matrix products, where Mi, 1≤ i ≤ r, has dimension
D(i-1)xD(i) (i.e. D(i-1) rows and D(i) columns). Let Mij denote
the product MixMi+1x …x Mj and C(i, j) be the cost of obtaining
an optimal product sequence for Mij. Observe that C(i,i) = 0,
1 ≤ i ≤ r, and that C(i, i+1) = D(i-1) D(i) D(i+1), 1 ≤ i < r.
1) Give the recurrence relation for C( i, j ), i < j.
(10%)
2) Sketch (or describe) how to solve the recurrence relation for
C(1, r). Your algorithm should be of complexity O(r3).(10%)
3
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