python實現Floyd演算法

下面是用Python實現Floyd演算法的程式碼：

# -*- coding: utf-8 -*-
"""
Created on Thu Jul 13 14:56:37 2017

@author: linzr
"""

## 表示無窮大
INF_val = 9999

class Floyd_Path():
    def __init__(self, node, node_map, path_map):
        self.node = node
        self.node_map = node_map
        self.node_length = len(node_map)
        self.path_map = path_map
        self._init_Floyd()
    
    def __call__(self, from_node, to_node):
        self.from_node = from_node
        self.to_node = to_node
        return self._format_path()

    def _init_Floyd(self):
        for k in range(self.node_length):
            for i in range(self.node_length):
                for j in range(self.node_length):
                    tmp = self.node_map[i][k] + self.node_map[k][j]
                    if self.node_map[i][j] > tmp:
                        self.node_map[i][j] = tmp
                        self.path_map[i][j] = self.path_map[i][k]
                        
        print '_init_Floyd is end'


    def _format_path(self):
        node_list = []
        temp_node = self.from_node
        obj_node = self.to_node
        print("the shortest path is: %d")%(self.node_map[temp_node][obj_node])
        node_list.append(self.node[temp_node])
        while True:
            node_list.append(self.node[self.path_map[temp_node][obj_node]])
            temp_node = self.path_map[temp_node][obj_node]
            if temp_node == obj_node:
                break;
        
        return node_list
                

        


def set_node_map(node_map, node, node_list, path_map):
    for i in range(len(node)):
        ## 對角線為0
        node_map[i][i] = 0
    for x, y, val in node_list:
        node_map[node.index(x)][node.index(y)] = node_map[node.index(y)][node.index(x)] = val
        path_map[node.index(x)][node.index(y)] = node.index(y)
        path_map[node.index(y)][node.index(x)] = node.index(x)

    
if __name__ == "__main__":
    node = ['A', 'B', 'C', 'D', 'E', 'F', 'G']
    node_list = [('A', 'F', 9), ('A', 'B', 10), ('A', 'G', 15), ('B', 'F', 2),
                 ('G', 'F', 3), ('G', 'E', 12), ('G', 'C', 10), ('C', 'E', 1),
                 ('E', 'D', 7)]
  
    ## node_map[i][j] 儲存i到j的最短距離
    node_map = [[INF_val for val in xrange(len(node))] for val in xrange(len(node))]
    ## path_map[i][j]=j 表示i到j的最短路徑是經過頂點j
    path_map = [[0 for val in xrange(len(node))] for val in xrange(len(node))]
    
    ## set node_map
    set_node_map(node_map, node, node_list, path_map)

 
    ## select one node to obj node, e.g. A --> D(node[0] --> node[3])
    from_node = node.index('A')
    to_node = node.index('E')
    Floydpath = Floyd_Path(node, node_map, path_map)
    path = Floydpath(from_node, to_node)
    print path

執行結果為：

the shortest path is: 23
['A', 'F', 'G', 'C', 'E']