diff --git a/graphs/floyd_warshall.py b/graphs/floyd_warshall.py index fae8b19b3..a1d12aac0 100644 --- a/graphs/floyd_warshall.py +++ b/graphs/floyd_warshall.py @@ -1,9 +1,16 @@ +# floyd_warshall.py +""" + The problem is to find the shortest distance between all pairs of vertices in a weighted directed graph that can + have negative edge weights. +""" + from __future__ import print_function -def printDist(dist, V): + +def _print_dist(dist, v): print("\nThe shortest path matrix using Floyd Warshall algorithm\n") - for i in range(V): - for j in range(V): + for i in range(v): + for j in range(v): if dist[i][j] != float('inf') : print(int(dist[i][j]),end = "\t") else: @@ -12,37 +19,84 @@ def printDist(dist, V): -def FloydWarshall(graph, V): - dist=[[float('inf') for i in range(V)] for j in range(V)] +def floyd_warshall(graph, v): + """ + :param graph: 2D array calculated from weight[edge[i, j]] + :type graph: List[List[float]] + :param v: number of vertices + :type v: int + :return: shortest distance between all vertex pairs + distance[u][v] will contain the shortest distance from vertex u to v. + + 1. For all edges from v to n, distance[i][j] = weight(edge(i, j)). + 3. The algorithm then performs distance[i][j] = min(distance[i][j], distance[i][k] + distance[k][j]) for each + possible pair i, j of vertices. + 4. The above is repeated for each vertex k in the graph. + 5. Whenever distance[i][j] is given a new minimum value, next vertex[i][j] is updated to the next vertex[i][k]. + """ + + dist=[[float('inf') for _ in range(v)] for _ in range(v)] - for i in range(V): - for j in range(V): + for i in range(v): + for j in range(v): dist[i][j] = graph[i][j] - for k in range(V): - for i in range(V): - for j in range(V): + # check vertex k against all other vertices (i, j) + for k in range(v): + # looping through rows of graph array + for i in range(v): + # looping through columns of graph array + for j in range(v): if dist[i][k]!=float('inf') and dist[k][j]!=float('inf') and dist[i][k]+dist[k][j] < dist[i][j]: dist[i][j] = dist[i][k] + dist[k][j] - printDist(dist, V) + _print_dist(dist, v) + return dist, v -#MAIN -V = int(input("Enter number of vertices: ")) -E = int(input("Enter number of edges: ")) +if __name__== '__main__': + v = int(input("Enter number of vertices: ")) + e = int(input("Enter number of edges: ")) -graph = [[float('inf') for i in range(V)] for j in range(V)] + graph = [[float('inf') for i in range(v)] for j in range(v)] -for i in range(V): - graph[i][i] = 0.0 + for i in range(v): + graph[i][i] = 0.0 -for i in range(E): - print("\nEdge ",i+1) - src = int(input("Enter source:")) - dst = int(input("Enter destination:")) - weight = float(input("Enter weight:")) - graph[src][dst] = weight + # src and dst are indices that must be within the array size graph[e][v] + # failure to follow this will result in an error + for i in range(e): + print("\nEdge ",i+1) + src = int(input("Enter source:")) + dst = int(input("Enter destination:")) + weight = float(input("Enter weight:")) + graph[src][dst] = weight -FloydWarshall(graph, V) + floyd_warshall(graph, v) + + + # Example Input + # Enter number of vertices: 3 + # Enter number of edges: 2 + + # # generated graph from vertex and edge inputs + # [[inf, inf, inf], [inf, inf, inf], [inf, inf, inf]] + # [[0.0, inf, inf], [inf, 0.0, inf], [inf, inf, 0.0]] + + # specify source, destination and weight for edge #1 + # Edge 1 + # Enter source:1 + # Enter destination:2 + # Enter weight:2 + + # specify source, destination and weight for edge #2 + # Edge 2 + # Enter source:2 + # Enter destination:1 + # Enter weight:1 + + # # Expected Output from the vertice, edge and src, dst, weight inputs!! + # 0 INF INF + # INF 0 2 + # INF 1 0