DATA STRUCTURES PROGRAM • GRAPHS

Find Unweighted Shortest-Path Distances with BFS

Learn how to find unweighted shortest-path distances with bfs using a clear C program.

IntermediateShortest pathUnweighted graphBFS

PROBLEM UNDERSTANDING

Input and expected output

Sample input

No input required

Sample output

0 1 1 2 2 3

COMPLETE C PROGRAM

Complete C implementation

#include <stdio.h>

int main(void)
{
    int graph[6][6] = {
        {0,1,1,0,0,0}, {1,0,0,1,0,0}, {1,0,0,1,1,0},
        {0,1,1,0,0,1}, {0,0,1,0,0,1}, {0,0,0,1,1,0}
    };
    int distance[6] = {-1,-1,-1,-1,-1,-1}, queue[6], front = 0, rear = 0;
    distance[0] = 0; queue[rear++] = 0;
    while (front < rear) {
        int vertex = queue[front++];
        for (int neighbour = 0; neighbour < 6; neighbour++)
            if (graph[vertex][neighbour] && distance[neighbour] < 0) {
                distance[neighbour] = distance[vertex] + 1; queue[rear++] = neighbour;
            }
    }
    for (int vertex = 0; vertex < 6; vertex++) printf("%d ", distance[vertex]);
    putchar('\n');
    return 0;
}

CURRENT STEP

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SELECTED LINE

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EXPECTED OUTPUT FOR THE SAMPLE

0 1 1 2 2 3

0%Step 0 of 0

PROGRAM EXPLANATION

Algorithm and explanation

Read the required input values.
The first BFS discovery gives the minimum edge count from the source.
Display the computed result.

The first BFS discovery gives the minimum edge count from the source.

EFFICIENCY

Time and space complexity

Time complexity

O(V²) with matrix

Auxiliary space

O(V)

DEBUGGING CHECKLIST

Common mistakes

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Use the correct format specifier for every variable.

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Initialize variables before using their values.

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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.