【算法日记】路径算法

此算法适合带有负边权的和无负边权的有向图。算法会计算出所有可能的路径和每个路径的长度

ways={
        "A":{
            "B":5,
            "C":2
        },
        "B":{
            "C":4
        },
        "C":{
            "D":5,
        },
        "D":None
    }

def findWay(ways,start,end):

    wayList={}

    def search(string):
        node=string[-1]
        if ways[node]:
            nodeList=ways[node].keys()
            for item in nodeList:
                if item==end:
                    wayList[string+item]=getValue(string+item)
                else:
                    newPath=string+item
                    search(newPath)

    def getValue(string):
        l=len(string)
        v=0
        for i in range(l-1):
            key1=string[i]
            key2=string[i+1]
            v+=int(ways[key1][key2])
        return v

    for key in ways[start]:
        new=start+key
        search(new)
    print wayList

findWay(ways,"A","D")

输出：

负边权图：

ways={
        "A":{
            "B":5,
            "C":2
        },
        "B":{
            "C":-4
        },
        "C":{
            "D":5,
        },
        "D":None
    }

def findWay(ways,start,end):

    wayList={}

    def search(string):
        node=string[-1]
        if ways[node]:
            nodeList=ways[node].keys()
            for item in nodeList:
                if item==end:
                    wayList[string+item]=getValue(string+item)
                else:
                    newPath=string+item
                    search(newPath)

    def getValue(string):
        l=len(string)
        v=0
        for i in range(l-1):
            key1=string[i]
            key2=string[i+1]
            v+=int(ways[key1][key2])
        return v

    for key in ways[start]:
        new=start+key
        search(new)
    print wayList

findWay(ways,"A","D")

输出：