Created
February 19, 2019 05:39
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| INF = float('inf') | |
| def bellman_ford(graph, weights, s): | |
| d = {v: INF for v in graph} | |
| d[s] = 0 | |
| pi = {s: None} | |
| edges = [(u, v) for u, vs in graph.items() for v in vs] | |
| for _ in range(len(graph) - 1): | |
| for (u, v) in edges: | |
| d_temp = d[u] + weights[u, v] | |
| if d_temp < d[v]: | |
| d[v] = d_temp | |
| pi[v] = u | |
| return d, pi | |
| if __name__ == '__main__': | |
| graph = {'A': ['B', 'C'], | |
| 'B': ['C', 'D', 'E'], | |
| 'C': [], | |
| 'D': ['B', 'C'], | |
| 'E': ['D']} | |
| weights = {('A', 'B'): -1, ('A', 'C'): 4, | |
| ('B', 'C'): 3, ('B', 'D'): 2, ('B', 'E'): 2, | |
| ('D', 'B'): 1, ('D', 'C'): 5, | |
| ('E', 'D'): -3} | |
| print(bellman_ford(graph, weights, 'A')) |
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