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If already a end distance is found, only ways which are shorter are calculated #15

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Falke-Design
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Thank you for your sharing Dijkstra's Algorithm in JavaScript!

I have found a small optimization with a big impact, but I don't know if it is compatible with the "thinking" / "logic" behind Dijkstra's Algorithm.

If already a end distance is found, it don't goes anymore over the node which are farer away then the distance to the end node. This makes it much fast if there are many nodes in the graph.

Current code:
shortest-path-slow

With optimization :
shortest-path-fast

parents[child] = node;

// if already a end distance is found, we allow only ways which are shorter
if (!distances[endNode] || distances[endNode] > distance) {
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This line is new

// save the distance to the object but if already a end distance is found, it must be shorter then it
// record the path
if ((!distances[child] || distances[child] > newdistance)
&& (!distances[endNode] || distances[endNode] > newdistance)) {
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and this line is new

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