DATA STRUCTURES PROGRAM • GRAPHS

Traverse a Graph with Breadth-First Search

Learn how to traverse a graph with breadth-first search using a clear C program.

IntermediateBFSQueueVisited

PROBLEM UNDERSTANDING

Input and expected output

Sample input

No input required

Sample output

0 1 2 3 4

COMPLETE C PROGRAM

Complete C implementation

#include <stdio.h>

int main(void)
{
    int graph[5][5] = {
        {0,1,1,0,0}, {1,0,0,1,0}, {1,0,0,1,1}, {0,1,1,0,0}, {0,0,1,0,0}
    };
    int visited[5] = {0}, queue[5], front = 0, rear = 0;
    visited[0] = 1; queue[rear++] = 0;
    while (front < rear) {
        int vertex = queue[front++];
        printf("%d ", vertex);
        for (int neighbour = 0; neighbour < 5; neighbour++)
            if (graph[vertex][neighbour] && !visited[neighbour]) {
                visited[neighbour] = 1; queue[rear++] = neighbour;
            }
    }
    putchar('\n');
    return 0;
}

CURRENT STEP

Select Start to walk through the important lines.

SELECTED LINE

No line selected

EXPECTED OUTPUT FOR THE SAMPLE

0 1 2 3 4

0%Step 0 of 0

PROGRAM EXPLANATION

Algorithm and explanation

Read the required input values.
Mark vertices when they enter the queue so each vertex is processed once.
Display the computed result.

Mark vertices when they enter the queue so each vertex is processed once.

EFFICIENCY

Time and space complexity

Time complexity

O(V²) with matrix

Auxiliary space

O(V)

DEBUGGING CHECKLIST

Common mistakes

Check this

Use the correct format specifier for every variable.

Check this

Initialize variables before using their values.

Check this

Check braces, semicolons and input order carefully.

Try it yourself

Practice: Run the program with the sample input, predict its output, and then test one boundary case of your own.