# Program for Shortest path using Dijkstra Algorithm in c++

### The following program illustrates the Shortest Path using Dijkstra Algorithm in C++:

```#include <iostream.h>
#include <conio.h>
#define MAX_NODE 50

struct node{
int vertex;
int weight;
node *next;
};

struct fringe_node{
int vertex;
fringe_node *next;
};

node *adj[MAX_NODE]; //For storing Adjacency list of nodes.int totNodes; //No. of Nodes in Graph.constint UNSEEN=1,FRINGE=2,INTREE=3; //status of node.int status[MAX_NODE];//status arr for maintaing status.
node *newl,*last;
int neighbours;
cout<<"nn---Graph Creation---nn";
cout<<"Enter total nodes in graph : ";
cin>>totNodes;
for(int i=1;i<=totNodes;i++){
last=NULL;
cout<<"Total Neighbours of "<<i<<" : ";
cin>>neighbours;
for(int j=1;j<=neighbours;j++){
newl=new node;
cout<<"Neighbour #"<<j<<" : ";
cin>>newl->vertex;
cout<<"Weight    #"<<j<<" : ";
cin>>newl->weight;
newl->next=NULL;
else{
last->next = newl;
last = newl;
}
}
}
}

//Insert node in a fring_list at Begining.void Insert_Beg(int item){
fringe_node *newl;
newl = new fringe_node;
newl->vertex = item;
newl->next = NULL;
newl->next = fringe_list;
fringe_list = newl;
}

//Delete element at pos position from fringe_list.void del(int pos){
//to points to previous node from where//to insertint i;
fringe_node *tmp,*delnode;
for(i=1,tmp=fringe_list; i < (pos-1); tmp=tmp->next,i++);

delnode = tmp->next;
tmp->next = tmp->next->next;
delete(delnode);
}

void print_path(int s,int d,int parent[]){
if(d==s)
cout<<"    "<<s;
else{
print_path(s,parent[d],parent);
cout<<"-->"<<d;
}
}

void shortestPath(){
int i,x,parent[MAX_NODE],edge_count,w,wt,v;
int min_dist,y,dist[MAX_NODE],stuck;
int source,destination;
node *ptr1;
fringe_node *ptr2;

cout<<"Enter Source Node : ";
cin>>source;
cout<<"Enter Destination Node : ";
cin>>destination;

fringe_list=NULL;
for(i=1;i<=totNodes;i++){
status[i]=UNSEEN;
parent[i]=0;
}

status[source]=INTREE;
dist[source]=0;
x=source;
stuck=0;
while( (x != destination) && (!stuck))
{
while(ptr1!=NULL){
y=ptr1->vertex;
wt=ptr1->weight;
if((status[y]==FRINGE) && (dist[x]+wt < dist[y]))
{
parent[y]=x;
dist[y] = dist[y] + wt;
}
elseif(status[y]==UNSEEN){
status[y]=FRINGE;
parent[y]=x;
dist[y] = dist[y] + wt;
Insert_Beg(y);
}
ptr1=ptr1->next;
}
if(fringe_list==NULL)
stuck=1;
else{
x=fringe_list->vertex;
min_dist=dist[x];
ptr2=fringe_list->next;
while(ptr2!=NULL){
w=ptr2->vertex;
if(dist[w] < min_dist)
{
x=w;
min_dist=dist[w];
}
ptr2=ptr2->next;
}
del(x);
status[x]=INTREE;
}
}
if(parent[destination]==0)
cout<<"No path from "<<source<<" to "<<destination;
else
{
cout<<"nnShortest Pathn";
print_path(source,destination,parent);
}
}

void main(){
clrscr();
cout<<"*****Minimum Spaning Tree (MST)*****n";
createGraph();
cout<<"n===Minimum Spaning Tree===n";
shortestPath();
getch();
}```