From 6500e7b9a975f5f51aba2a476595b4408285ab94 Mon Sep 17 00:00:00 2001
From: Akhil Baiju <45595599+akhilbaiju@users.noreply.github.com>
Date: Sun, 31 Oct 2021 17:28:22 +0530
Subject: [PATCH] =?UTF-8?q?Dijkstra=E2=80=99s=20Algorithm=20in=20C?=
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Dijkstra algorithm is also called single source shortest path algorithm. It is based on greedy technique. The algorithm maintains a list visited[ ] of vertices, whose shortest distance from the source is already known.
---
 Dijkstra Algorithm.c | 82 ++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 82 insertions(+)
 create mode 100644 Dijkstra Algorithm.c

diff --git a/Dijkstra Algorithm.c b/Dijkstra Algorithm.c
new file mode 100644
index 00000000..81298d36
--- /dev/null
+++ b/Dijkstra Algorithm.c	
@@ -0,0 +1,82 @@
+#include<stdio.h>
+#include<conio.h>
+#define INFINITY 9999
+#define MAX 10
+ 
+void dijkstra(int G[MAX][MAX],int n,int startnode);
+ 
+int main()
+{
+int G[MAX][MAX],i,j,n,u;
+printf("Enter no. of vertices:");
+scanf("%d",&n);
+printf("\nEnter the adjacency matrix:\n");
+for(i=0;i<n;i++)
+for(j=0;j<n;j++)
+scanf("%d",&G[i][j]);
+printf("\nEnter the starting node:");
+scanf("%d",&u);
+dijkstra(G,n,u);
+return 0;
+}
+ 
+void dijkstra(int G[MAX][MAX],int n,int startnode)
+{
+ 
+int cost[MAX][MAX],distance[MAX],pred[MAX];
+int visited[MAX],count,mindistance,nextnode,i,j;
+//pred[] stores the predecessor of each node
+//count gives the number of nodes seen so far
+//create the cost matrix
+for(i=0;i<n;i++)
+for(j=0;j<n;j++)
+if(G[i][j]==0)
+cost[i][j]=INFINITY;
+else
+cost[i][j]=G[i][j];
+//initialize pred[],distance[] and visited[]
+for(i=0;i<n;i++)
+{
+distance[i]=cost[startnode][i];
+pred[i]=startnode;
+visited[i]=0;
+}
+distance[startnode]=0;
+visited[startnode]=1;
+count=1;
+while(count<n-1)
+{
+mindistance=INFINITY;
+//nextnode gives the node at minimum distance
+for(i=0;i<n;i++)
+if(distance[i]<mindistance&&!visited[i])
+{
+mindistance=distance[i];
+nextnode=i;
+}
+//check if a better path exists through nextnode
+visited[nextnode]=1;
+for(i=0;i<n;i++)
+if(!visited[i])
+if(mindistance+cost[nextnode][i]<distance[i])
+{
+distance[i]=mindistance+cost[nextnode][i];
+pred[i]=nextnode;
+}
+count++;
+}
+ 
+//print the path and distance of each node
+for(i=0;i<n;i++)
+if(i!=startnode)
+{
+printf("\nDistance of node%d=%d",i,distance[i]);
+printf("\nPath=%d",i);
+j=i;
+do
+{
+j=pred[j];
+printf("<-%d",j);
+}while(j!=startnode);
+}
+}