Dynamic Programming · Algorithms · GATE CSE

The Floyd-Warshall algorithm for all-pair shortest paths computation is based on

Match the following:

List 1

(P) Prim’s algorithm for minimum spanning tree
(Q) Floyd-Warshall algorithm for all pairs shortest paths
(R) Mergesort
(S) Hamiltonian circuit

List 2

(i) Backtracking
(ii) Greedy method
(iii) Dynamic programming
(iv) Divide and conquer

An algorithm to find the length of the longest monotonically increasing sequence of numbers in an array A[0:n−1] is given below.

Let L_i, denote the length of the longest monotonically increasing sequence starting at index i in the array. Initialize L_n−1=1.

For all i such that $$0 \leq i \leq n-2$$

$$L_i = \begin{cases} 1+ L_{i+1} & \quad\text{if A[i] < A[i+1]} \\ 1 & \quad\text{Otherwise}\end{cases}$$

Finally, the length of the longest monotonically increasing sequence is max(L₀, L₁,…,L_n−1)
Which of the following statements is TRUE?

The tightest lower bound on the number of comparisons, in the worst case, for comparison-based sorting is of the order of

Which one of the following algorithm design techniques is used in finding all pairs of shortest distances in a graph?

Let G(V, E) be a directed graph, where V = {1, 2, 3, 4, 5} is the set of vertices and E is the set of directed edges, as defined by the following adjacency matrix A.

$$A[i][j] = \left\{ {\matrix{ {1,} & {1 \le j \le i \le 5} \cr {0,} & {otherwise} \cr } } \right.$$

A[i][j] = 1 indicates a directed edge from node i to node j. A directed spanning tree of G, rooted at r $$\in$$ V, is defined as a subgraph T of G such that the undirected version of T is a tree, and T contains a directed path from r to every other vertex in V. The number of such directed spanning trees rooted at vertex 5 is _____________.

Consider the following directed graph: 

Which of the following is/are correct about the graph?

Define R_n to be the maximum amount earned by cutting a rod of length n meters into one or more pieces of integer length and selling them. For i > 0, let p[i] denotes the selling price of a rod whose length is i meters. Consider the array of prices:

p[1] = 1, p[2] = 5, p[3] = 8, p[4] = 9, p[5] = 10, p[6] = 17, p[7] = 18

Which of the following statements is/are correct about R₇?

Assume that multiplying a matrix $${G_1}$$ of dimension $$p \times q$$ with another matrix $${G_2}$$ of dimension $$q \times r$$ requires $$pqr$$ scalar multiplications. Computing the product of $$n$$ matrices $${G_1}{G_2}{G_{3...}}{G_n}$$ can be done by parenthesizing in different ways. Define $${G_i}\,\,{G_{i + 1}}$$ as an explicitly computed pair for a given paranthesization if they are directly multiplied. For example, in the matrix multiplication chain $${G_1}{G_2}{G_3}{G_4}{G_5}{G_6}$$ using parenthesization $$\left( {{G_1}\left( {{G_2}{G_3}} \right)} \right)\left( {{G_4}\left( {{G_5}{G_6}} \right)} \right),\,\,{G_2}{G_3}$$ and $${G_5}{G_6}$$ are the only explicitly computed pairs.

Consider a matrix multiplication chain $${F_1}{F_2}{F_3}{F_4}{F_5},$$ where matrices $${F_1},{F_2},{F_3},{F_4}$$ and $${F_5}$$ are of dimensions $$2 \times 25,\,\,25 \times 3,\,\,3 \times 16,\,\,16 \times 1$$ and $$1 \times 1000,$$ respectively. In the parenthesization of $${F_1}{F_2}{F_3}{F_4}{F_5}$$ that minimizes the total number of scalar multiplications, the explicitly computed pairs is/are

Let $${A_1},{A_2},{A_3},$$ and $${A_4}$$ be four matrices of dimensions $$10 \times 5,\,\,5 \times 20,\,\,20 \times 10,$$ and $$10 \times 5,\,$$ respectively. The minimum number of scalar multiplications required to find the product $${A_1}{A_2}{A_3}{A_4}$$ using the basic matrix multiplication method is ______________.

Given below are some algorithms, and some algorithm design paradigms.

GROUP 1	GROUP 2
1. Dijkstra's Shortest Path	i. Divide and Conquer
2. Floyd-Warshall algorithm to compute all pairs shortest path	ii. Dynamic Programming
3. Binary search on a sorted array	iii. Greedy design
4. Backtracking search on a graph	iv. Depth-first search
	v. Breadth-first search

Match the above algorithms on the left to the corresponding design paradigm they follow.

Consider two strings A = “qpqrr” and B = “pqprqrp”. Let x be the length of the longest common subsequence (not necessarily contiguous) between A and B and let y be the number of such longest common subsequences between A and B. Then x + 10y = ___.

Four matrices M₁, M₂, M₃ and M₄ of dimensions p $$\times$$ q, q $$\times$$ r, r $$\times$$ s and s $$\times$$ t respectively can be multiplied is several ways with different number of total scalar multiplications. For example, when multiplied as ((M₁ $$\times$$ M₂) $$\times$$ (M₃ $$\times$$ M₄)), the total number of multiplications is pqr + rst + prt. When multiplied as (((M₁ $$\times$$ M₂) $$\times$$ M₃) $$\times$$ M₄), the total number of scalar multiplications is pqr + prs + pst.

If p = 10, q = 100, r = 20, s = 5 and t = 80, then the number of scalar multiplications needed is:

A sub-sequence of a given sequence is just the given sequence with some elements (possibly none or all) left out. We are given two sequences X[m] and Y[n] of lengths m and n, respectively with indexes of X and Y starting from 0.

We wish to find the length of the longest common sub-sequence (LCS) of X[m] and Y[n] as l(m,n), where an incomplete recursive definition for the function I(i,j) to compute the length of the LCS of X[m] and Y[n] is given below:

l(i,j)  = 0, if either i = 0 or j = 0
        = expr1, if i,j > 0 and X[i-1] = Y[j-1]
        = expr2, if i,j > 0 and X[i-1] ≠ Y[j-1]

Which one of the following options is correct?

A sub-sequence of a given sequence is just the given sequence with some elements (possibly none or all) left out. We are given two sequences X[m] and Y[n] of lengths m and n, respectively with indexes of X and Y starting from 0.

We wish to find the length of the longest common sub-sequence (LCS) of X[m] and Y[n] as l(m,n), where an incomplete recursive definition for the function I(i,j) to compute the length of the LCS of X[m] and Y[n] is given below:

l(i,j)  = 0, if either i = 0 or j = 0
        = expr1, if i,j > 0 and X[i-1] = Y[j-1]
        = expr2, if i,j > 0 and X[i-1] ≠ Y[j-1]

The value of l(i, j) could be obtained by dynamic programming based on the correct recursive definition of l(i, j) of the form given above, using an array L[M, N], where M = m+1 and N = n + 1, such that L[i, j] = l(i, j).

Which one of the following statements would be TRUE regarding the dynamic programming solution for the recursive definition of l(i, j)?

The subset-sum problem is defined as follows. Given a set of n positive integers, S = {a₁ ,a₂ ,a₃ ,…,a_n} and positive integer W, is there a subset of S whose elements sum to W? A dynamic program for solving this problem uses a 2-dimensional Boolean array X, with n rows and W+1 columns. X[i, j], 1 <= i <= n, 0 <= j <= W, is TRUE if and only if there is a subset of {a₁ ,a₂ ,…,a_i} whose elements sum to j.

Which entry of the array X, if TRUE, implies that there is a subset whose elements sum to W?

The subset-sum problem is defined as follows. Given a set of n positive integers, S = {a₁ ,a₂ ,a₃ ,…,a_n} and positive integer W, is there a subset of S whose elements sum to W? A dynamic program for solving this problem uses a 2-dimensional Boolean array X, with n rows and W+1 columns. X[i, j], 1 <= i <= n, 0 <= j <= W, is TRUE if and only if there is a subset of {a₁ ,a₂ ,…,a_i} whose elements sum to j.
Which of the following is valid for 2 <= i <= n and ai <= j <= W?

Consider the following C program that attempts to locate an element x in an array Y[] using binary search. The program is erroneous.

1.   f(int Y[10], int x) {
2.     int i, j, k;
3.     i = 0; j = 9;
4.     do {
5.             k =  (i + j) /2;
6.             if( Y[k] < x)  i = k; else j = k;
7.         } while(Y[k] != x && i < j);
8.     if(Y[k] == x) printf ("x is in the array ") ;
9.     else printf (" x is not in the array ") ;
10.  }

On which of the following contents of Y and x does the program fail?

Consider the following C program that attempts to locate an element x in an array Y[] using binary search. The program is erroneous.

1.   f(int Y[10], int x) {
2.     int i, j, k;
3.     i = 0; j = 9;
4.     do {
5.             k =  (i + j) /2;
6.             if( Y[k] < x)  i = k; else j = k;
7.         } while(Y[k] != x && i < j);
8.     if(Y[k] == x) printf ("x is in the array ") ;
9.     else printf (" x is not in the array ") ;
10.  }

The correction needed in the program to make it work properly is

A binary search tree is generated by inserting in order the following integers:

50, 15, 62, 5, 20, 58, 91, 3, 8, 37, 60, 24

The number of nodes in the left subtree and right subtree of the root respectively is

Obtain the optimal binary search tree with equal probabilities for the identifier set (a₁, a₂, a₃) = ( if, stop, while)