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【代码随想录算法训练营——Day60】图论——94.城市间货物运输I、95.城市间货物运输II、96.城市间货物运输III

news 2025/11/7 9:12:00

卡码网题目链接
https://kamacoder.com/problempage.php?pid=1152
https://kamacoder.com/problempage.php?pid=1153
https://kamacoder.com/problempage.php?pid=1154

题解
94.城市间货物运输I
和昨天那题思路类似，加了个队列优化，仿照着c++代码写的。

95.城市间货物运输II
具体看题解，代码也是仿照题解写的。

96.城市间货物运输III
看题解的感悟：理解思路挺重要，还有了4个拓展，联系了前几天的算法。
代码部分：要加updated更新记录，防止时间超限，题解也是这么写的

代码

#94.城市间货物运输I
from collections import deque
class Edge():def __init__(self, to, val):self.to = toself.val = valif __name__ == "__main__":n, m = map(int, input().split())graph = [[] for _ in range(n + 1)]isInQueue = [False] * (n + 1)for _ in range(m):s, t, v = map(int, input().split())graph[s].append(Edge(t, v))start = 1end = nminDist = [float('inf')] * (n + 1)minDist[start] = 0queue = deque()queue.append(start)isInQueue[start] = Truewhile queue:node = queue.popleft()isInQueue[node] = Falsefor edge in graph[node]:fromm, to, val = node, edge.to, edge.valif minDist[to] > minDist[fromm] + val:minDist[to] = minDist[fromm] + valif isInQueue[to] == False:queue.append(to)isInQueue[to] = Trueif minDist[end] == float('inf'):print("unconnected")else:print(minDist[end])

#95.城市间货物运输II
if __name__ == "__main__":n, m = map(int, input().split())graph = []for _ in range(m):graph.append(list(map(int, input().split())))minDist = [float('inf')] * (n + 1)start, end = 1, nminDist[start] = 0flag = Falsefor i in range(1, n + 1): # 多循环一次for side in graph:fromm, to, val = side[0], side[1], side[2]if i < n:if minDist[fromm] != float('inf') and minDist[to] > minDist[fromm] + val:minDist[to] = minDist[fromm] + valelse:if minDist[fromm] != float('inf') and minDist[to] > minDist[fromm] + val:flag = Trueif flag:print("circle")elif minDist[end] == float('inf'):print("unconnected")else:print(minDist[end])

#96.城市间货物运输III
if __name__ == "__main__":n, m = map(int, input().split())graph = []for _ in range(m):graph.append(list(map(int, input().split())))src, dst, k = map(int, input().split())minDist = [float('inf')] * (n + 1)minDist[src] = 0for i in range(k + 1):updated = FalseminDist_copy = minDist.copy()for side in graph:fromm, to, val = side[0], side[1], side[2]if minDist_copy[fromm] != float('inf') and minDist[to] > minDist_copy[fromm] + val:minDist[to] = minDist_copy[fromm] + valupdated = Trueif not updated:breakif minDist[dst] == float('inf'):print("unreachable")else:print(minDist[dst])