single source shortest path algorithm geeksforgeeks code example

Example 1: dijkstra algorithm c++

#include<bits/stdc++.h>
using namespace std;

int main()
{
	int n = 9;
	
	int mat[9][9] = { { 100,4,100,100,100,100,100,8,100}, 
                      { 4,100,8,100,100,100,100,11,100}, 
                      {100,8,100,7,100,4,100,100,2}, 
                      {100,100,7,100,9,14,100,100,100}, 
                      {100,100,100,9,100,100,100,100,100}, 
                      {100,100,4,14,10,100,2,100,100}, 
                      {100,100,100,100,100,2,100,1,6}, 
                      {8,11,100,100,100,100,1,100,7}, 
                      {100,100,2,100,100,100,6,7,100}};
	
	int src = 0;
	int count = 1;
	
	int path[n];
	for(int i=0;i<n;i++)
		path[i] = mat[src][i];
	
	int visited[n] = {0};
	visited[src] = 1;
	
	while(count<n)
	{
		int minNode;
		int minVal = 100;
		
		for(int i=0;i<n;i++)
			if(visited[i] == 0 && path[i]<minVal)
			{
				minVal = path[i];
				minNode = i;
			}
		
		visited[minNode] = 1;
		
		for(int i=0;i<n;i++)
			if(visited[i] == 0)
				path[i] = min(path[i],minVal+mat[minNode][i]);
					
		count++;
	}
	
	path[src] = 0;
	for(int i=0;i<n;i++)
		cout<<src<<" -> "<<path[i]<<endl;
	
	return(0);
}

Example 2: Dijkstra's Weighted Graph Shortest Path in c++

#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; 
} 
  

void printSolution(int dist[]) 
{ 
    printf("Vertex \t\t Distance from Source\n"); 
    for (int i = 0; i < V; i++) 
        printf("%d \t\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); 
} 
  

int main() 
{ 
    
    int graph[V][V] = { { 0, 4, 0, 0, 0, 0, 0, 8, 0 }, 
                        { 4, 0, 8, 0, 0, 0, 0, 11, 0 }, 
                        { 0, 8, 0, 7, 0, 4, 0, 0, 2 }, 
                        { 0, 0, 7, 0, 9, 14, 0, 0, 0 }, 
                        { 0, 0, 0, 9, 0, 10, 0, 0, 0 }, 
                        { 0, 0, 4, 14, 10, 0, 2, 0, 0 }, 
                        { 0, 0, 0, 0, 0, 2, 0, 1, 6 }, 
                        { 8, 11, 0, 0, 0, 0, 1, 0, 7 }, 
                        { 0, 0, 2, 0, 0, 0, 6, 7, 0 } }; 
  
    dijkstra(graph, 0); 
  
    return 0; 
}