#289 add floyd warshall algorithm #302
Conversation
…in dijsktra algorithm
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Could you please resolve the conflicts? |
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What things to change? |
Codecov Report
@@ Coverage Diff @@
## master #302 +/- ##
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+ Coverage 98.855% 98.866% +0.011%
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Files 25 25
Lines 2970 2999 +29
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+ Hits 2936 2965 +29
Misses 34 34
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pydatastructs/graphs/algorithms.py
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| @@ -762,6 +767,40 @@ def _dijkstra_adjacency_list(graph: Graph, start: str, target: str): | |||
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| _dijkstra_adjacency_matrix = _dijkstra_adjacency_list | |||
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| def _floyd_warshall_adjacency_list(graph: Graph, source: str, target: str): | |||
| dist, predecessor, dist_temp, pred_temp = dict(), dict(), dict(), dict() | |||
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I am unable to understand the purpose of dist_temp, pred_temp. In L778 to L780 if they are being copied to dist[v] and predecessor[v]. May be, we could have directly followed, https://en.wikipedia.org/wiki/Floyd%E2%80%93Warshall_algorithm#Pseudocode_[11] word to word.
| _test_shortest_paths("List", 'floyd_warshall') | ||
| _test_shortest_paths("Matrix", 'floyd_warshall') |
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floyd_warshall is a pair wise shortest path algorithm so tests of dijkstra and bellman_ford may not work. As can be seen, API for both are different.
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We need to define, |
References to other Issues or PRs or Relevant literature
Fixes #289
Brief description of what is fixed or changed
I added _floyd_warshall_adjacency_list function and _floyd_warshall_adjacency_matrix function in pydatastructs.graphs.algorithms to determine the distances and predecessors for given source and target.
Added shortest_path construction function to construct the shortest path from the predecessor's details determined using the function _floyd_warshall_adjacency_list or _floyd_warshall_adjacency_matrix.
In that floyd_warshall algorithm, function added conditions for checking infinity cases to avoid unnecessary computations when adding with other valid numbers.
Other comments
The Floyd-Warshall algorithm can be applied on a graph in a way similar to that of the Bellman-Ford algorithm.
Example: shortest_paths(G, 'floyd_warshall', 'V1')
A small modification will be required in the shortest_paths function in order to utilize the all pair shortest path advantage of the Floyd-Warshall algorithm. The current implementation of shortest_paths function supports only the single-source shortest path nature of the Bellman-Ford algorithm.
It works for both Source and target cases and also Dynamic programming approach is used. That condition checking of infinity helps to avoid key_error problems.