Graph Terminology Vertices Edges Directed Undirected Weighted in DSA C - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare a graph vertex structure with an integer id.

DSA C

typedef struct Vertex {
    int [1];
} Vertex;

Drag options to blanks, or click blank then click option'

Avalue

Bweight

Cedge

Did

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'weight' or 'edge' as the vertex identifier field.

Using a generic name like 'value' instead of 'id'.

The vertex structure should have an integer id to uniquely identify it.

2fill in blank

medium

Complete the code to declare an edge structure with source and destination vertices.

DSA C

typedef struct Edge {
    int source;
    int [1];
} Edge;

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Aweight

Bdestination

Cid

Dvertex

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'weight' instead of the destination vertex.

Using 'id' or 'vertex' which are not correct here.

The edge connects a source vertex to a destination vertex.

3fill in blank

hard

Fix the error in the code to correctly declare a weighted edge structure.

DSA C

typedef struct WeightedEdge {
    int source;
    int destination;
    float [1];
} WeightedEdge;

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Aweight

Bid

Cvalue

Dcost

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'id' or 'value' which are ambiguous.

Using 'cost' which is less common in this context.

The field representing the edge's weight should be named weight.

4fill in blank

hard

Fill both blanks to complete the function that checks if a graph is directed or undirected based on edges.

DSA C

int isDirectedGraph(Edge edges[], int n) {
    for (int i = 0; i < n; i++) {
        int src = edges[i].source;
        int dest = edges[i].[1];
        int found = 0;
        for (int j = 0; j < n; j++) {
            if (edges[j].source == dest && edges[j].[2] == src) {
                found = 1;
                break;
            }
        }
        if (!found) return 1; // Directed
    }
    return 0; // Undirected
}

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Adestination

Bweight

Csource

Did

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'weight' or 'id' instead of 'destination' causes logic errors.

Mixing source and destination fields incorrectly.

The function compares edges by their destination and source fields to check for reverse edges.

5fill in blank

hard

Fill all three blanks to complete the function that creates a weighted edge and assigns values.

DSA C

WeightedEdge createWeightedEdge(int [1], int [2], float [3]) {
    WeightedEdge e;
    e.source = [1];
    e.destination = [2];
    e.weight = [3];
    return e;
}

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Asrc

Bdest

Cw

Dcost

Attempts:

3 left

💡 Hint

Common Mistakes

Using inconsistent parameter names that don't match the assignments.

Using 'cost' instead of 'w' for weight parameter.

The function parameters are named src, dest, and w to assign source, destination, and weight respectively.

Practice

1. Which of the following best describes a vertex in a graph?

easy

A. A point or node representing an entity in the graph

B. A connection between two nodes

C. A path that starts and ends at the same node

D. A graph with no edges

Solution

1. Step 1: Understand the definition of vertex

   A vertex is a fundamental unit in a graph representing an entity or point.

2. Step 2: Differentiate vertex from edges and other terms

   Edges connect vertices; paths and graph types are different concepts.

3. Final Answer:

   A point or node representing an entity in the graph -> Option A

4. Quick Check:

   Vertex = node/entity [OK]

Hint: Vertices are the points or nodes in a graph [OK]

Common Mistakes:

• Confusing vertices with edges
• Thinking vertices are paths
• Mixing vertex with graph types

2. Which of the following is the correct way to represent a weighted edge from vertex u to vertex v with weight 5 in C struct?

easy

A. struct Edge { int u, v; }; struct Weight { int w; };

B. struct Edge { int u; int v; }; int weight = 5;

C. struct Edge { int u; int v; int weight; };

D. struct Edge { int u; int v; };

Solution

1. Step 1: Identify the correct struct fields for weighted edge

   A weighted edge needs source vertex, destination vertex, and weight as fields.

2. Step 2: Check struct syntax correctness

   struct Edge { int u; int v; int weight; }; correctly declares all three fields in one struct.

3. Final Answer:

   struct Edge { int u; int v; int weight; }; -> Option C

4. Quick Check:

   Weighted edge struct = u, v, weight [OK]

Hint: Weighted edges need u, v, and weight fields in one struct [OK]

Common Mistakes:

• Separating weight outside the edge struct
• Incorrect field order causing confusion
• Missing weight field

3. What is the output of the following code snippet that prints edges of a directed weighted graph?

typedef struct { int u; int v; int weight; } Edge;
Edge edges[] = { {0, 1, 10}, {1, 2, 20}, {2, 0, 30} };
int n = 3;
for (int i = 0; i < n; i++) {
    printf("%d -> %d (weight %d)\n", edges[i].u, edges[i].v, edges[i].weight);
}

medium

A. 0 -> 1 (weight 10)
1 -> 2 (weight 30)
2 -> 0 (weight 20)

B. 0 -> 1 (weight 10)
1 -> 2 (weight 20)
2 -> 0 (weight 30)

C. 0 -> 1 (weight 30)
1 -> 2 (weight 20)
2 -> 0 (weight 10)

D. 1 -> 0 (weight 10)
2 -> 1 (weight 20)
0 -> 2 (weight 30)

Solution

1. Step 1: Read the edges array values

   Edges are: (0,1,10), (1,2,20), (2,0,30).

2. Step 2: Trace the loop printing each edge

   Loop prints each edge in order with format "u -> v (weight w)".

3. Final Answer:

   0 -> 1 (weight 10) 1 -> 2 (weight 20) 2 -> 0 (weight 30) -> Option B

4. Quick Check:

   Print edges as stored = 0 -> 1 (weight 10) 1 -> 2 (weight 20) 2 -> 0 (weight 30) [OK]

Hint: Print edges in array order with their weights [OK]

Common Mistakes:

• Reversing u and v in print
• Mixing up weights between edges
• Printing edges in wrong order

4. Identify the error in this code snippet that tries to create an undirected graph edge list:

typedef struct { int u; int v; } Edge;
Edge edges[2];
edges[0].u = 0; edges[0].v = 1;
edges[1].u = 1; edges[1].v = 0;
// Print edges
for (int i = 0; i <= 2; i++) {
    printf("Edge from %d to %d\n", edges[i].u, edges[i].v);
}

medium

A. Edge direction is incorrect for undirected graph

B. Edges should have weight field

C. Edges array size should be 1, not 2

D. Loop condition should be i < 2, not i <= 2

Solution

1. Step 1: Check array size and loop bounds

   Edges array has size 2, valid indices are 0 and 1.

2. Step 2: Identify loop error

   Loop runs from i=0 to i=2 inclusive, which accesses edges[2] (out of bounds).

3. Final Answer:

   Loop condition should be i < 2, not i <= 2 -> Option D

4. Quick Check:

   Array size 2 means max index 1 [OK]

Hint: Loop index must be less than array size [OK]

Common Mistakes:

• Using <= instead of < in loop
• Assuming edges need weight for undirected
• Confusing edge direction in undirected graphs

5. You have a weighted undirected graph with vertices 0, 1, 2 and edges:
(0,1,4), (1,2,6), (0,2,5)
How many edges will be stored if you represent this graph using an edge list storing each edge only once?

medium

A. 3

B. 6

C. 2

D. 1

Solution

1. Step 1: Understand undirected edge storage

   In undirected graphs, each edge connects two vertices without direction, so store only one entry per edge.

2. Step 2: Count unique edges given

   Edges are (0,1), (1,2), (0,2) -- total 3 unique edges.

3. Final Answer:

   3 -> Option A

4. Quick Check:

   Undirected edges stored once = 3 [OK]

Hint: Undirected edges stored once, count unique pairs [OK]

Common Mistakes:

• Counting each edge twice
• Confusing directed with undirected storage
• Ignoring weights when counting edges