SDE - 1

Dijkstra's Algorithm basically starts at the source node and it analyzes the graph to find the shortest path between that node and all the other nodes in the graph.
The algorithm keeps track of the currently known shortest distance from each node to the source node and it updates these values if it finds a shorter path.
Once the shortest path between the source node and another node is found, that node is marked as "visited" and added to the path. 
The process continues until all the nodes in the graph have been added to the path. This way, we have a path that connects the source node to all other nodes following the shortest path possible to reach each node.

Pseudocode :

function Dijkstra(Graph, source) :
2: for each vertex v in Graph: // Initialization
3: dist[v] := infinity // initial distance from source to vertex v is set to infinite
4: previous[v] := undefined // Previous node in optimal path from source
5: dist[source] := 0 // Distance from source to source
6: Q := the set of all nodes in Graph // all nodes in the graph are unoptimized - thus are in Q
7: while Q is not empty: // main loop
8: u := node in Q with smallest dist[ ]
9: remove u from Q
10: for each neighbor v of u: // where v has not yet been removed from Q.
11: alt := dist[u] + dist_between(u, v)
12: if alt < dist[v] // Relax (u,v)
13: dist[v] := alt
14: previous[v] := u
15: return previous[ ]

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