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We get a graph with a source vertex. We have to find the shortest path from the source vertex to all other vertices of the graph.
Dijikstra's algorithm is a greedy algorithm for finding the shortest path from a source vertex to the root node of a graph to the root node of the graph.
Step 1 : Create a set shortPath to store vertices that come in the way of the shortest path tree. Step 2 : Initialize all distance values as INFINITE and assign distance values as 0 for source vertex so that it is picked first. Step 3 : Loop until all vertices of the graph are in the shortPath. Step 3.1 : Take a new vertex that is not visited and is nearest. Step 3.2 : Add this vertex to shortPath. Step 3.3 : For all adjacent vertices of this vertex update distances. Now check every adjacent vertex of V, if sum of distance of u and weight of edge is elss the update it.
Let us create a program based on this algorithm.
#include <limits.h> #include <stdio.h> #define V 9 int minDistance(int dist[], bool sptSet[]) { int min = INT_MAX, min_index; for (int v = 0; v < V; v++) if (sptSet[v] == false && dist[v] <= min) min = dist[v], min_index = v; return min_index; } int printSolution(int dist[], int n) { printf("Vertex Distance from Source\n"); for (int i = 0; i < V; i++) printf("%d \t %d\n", i, dist[i]); } void dijkstra(int graph[V][V], int src) { int dist[V]; bool sptSet[V]; for (int i = 0; i < V; i++) dist[i] = INT_MAX, sptSet[i] = false; dist[src] = 0; for (int count = 0; count < V - 1; count++) { int u = minDistance(dist, sptSet); sptSet[u] = true; for (int v = 0; v < V; v++) if (!sptSet[v] && graph[u][v] && dist[u] != INT_MAX && dist[u] + graph[u][v] < dist[v]) dist[v] = dist[u] + graph[u][v]; } printSolution(dist, V); } int main() { int graph[V][V] = { { 0, 6, 0, 0, 0, 0, 0, 8, 0 }, { 6, 0, 8, 0, 0, 0, 0, 13, 0 }, { 0, 8, 0, 7, 0, 6, 0, 0, 2 }, { 0, 0, 7, 0, 9, 14, 0, 0, 0 }, { 0, 0, 0, 9, 0, 10, 0, 0, 0 }, { 0, 0, 6, 14, 10, 0, 2, 0, 0 }, { 0, 0, 0, 0, 0, 2, 0, 1, 6 }, { 8, 13, 0, 0, 0, 0, 1, 0, 7 }, { 0, 0, 2, 0, 0, 0, 6, 7, 0 } }; dijkstra(graph, 0); return 0; }
Vertex Distance from Source 0 0 1 6 2 14 3 21 4 21 5 11 6 9 7 8 8 15
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