Python实现Pat 1028. List Sorting (25)-蒲公英云

Python实现Pat 1028. List Sorting (25)

水深无声 2022-06-04 08:14 292阅读 0赞

题目

A traveler’s map gives the distances between cities along the highways, together with the cost of each highway. Now you are supposed to write a program to help a traveler to decide the shortest path between his/her starting city and the destination. If such a shortest path is not unique, you are supposed to output the one with the minimum cost, which is guaranteed to be unique.

Input Specification:

Each input file contains one test case. Each case starts with a line containing 4 positive integers N, M, S, and D, where N (<=500) is the number of cities (and hence the cities are numbered from 0 to N-1); M is the number of highways; S and D are the starting and the destination cities, respectively. Then M lines follow, each provides the information of a highway, in the format:

City1 City2 Distance Cost

where the numbers are all integers no more than 500, and are separated by a space.

Output Specification:

For each test case, print in one line the cities along the shortest path from the starting point to the destination, followed by the total distance and the total cost of the path. The numbers must be separated by a space and there must be no extra space at the end of output.

Sample Input
4 5 0 3
0 1 1 20
1 3 2 30
0 3 4 10
0 2 2 20
2 3 1 20
Sample Output
0 2 3 3 40

#树或者图的遍历。注意Python里list的list的初始化，避免浅复制
def dfs(s,dist,cost):
    global D,path,minD,minP,minC
    if s==D:
        if dist<minD or (dist==minD and cost<minC) :
            minD=dist
            minC=cost
            minP=path[:]
        return
    elif dist>minD:
        return
    else:
        for p in tree[s]:
            if visit[p]==False:
                visit[p]=True
                path.append(p)
                dfs(p,dist+dists[s][p],cost+costs[s][p])
                visit[p]=False
                path.pop()
    return
MAX=10000
N,M,S,D=[int(x) for x in input().split(' ')]
visit=[False]*(N)
tree={}
dists=[]
costs=[]
tmp=[MAX]*N
for i in range(M):
    dists.append(tmp[:])
    costs.append(tmp[:])
for i in range(N):
    tree[i]=[]
for i in range(M):
    a,b,c,d=[int(x) for x in input().split(' ')]
    tree[a].append(b)
    tree[b].append(a)
    dists[a][b]=c
    dists[b][a]=c
    costs[a][b]=d
    costs[b][a]=d
path=[]
minP=[]
cost=0
dist=0
minC=MAX
minD=MAX
visit[S]=True
path.append(S)
dfs(S,dist,cost)
for p in minP:
    print(p,end=' ')
print (minD,minC)