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Commit e94a5fb

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author
hj.tian
committed
feat: add LeetCode75 day26
feat: add LeetCode75 day26
1 parent 5c65370 commit e94a5fb

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2 files changed

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‎leetcode75/day26_210.py

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from collections import defaultdict
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from typing import List
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class Solution:
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def findOrder(self, numCourses: int, prerequisites: List[List[int]]) -> List[int]:
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digraph = defaultdict(list)
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in_degree = [0 for _ in range(numCourses)]
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# 构建有向图
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for dependcy in prerequisites:
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# 0: [1, 2]
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digraph[dependcy[1]].append(dependcy[0])
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in_degree[dependcy[0]] += 1
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# 广度优先搜索
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result = []
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queue = [index for index in range(numCourses) if in_degree[index] == 0]
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while queue:
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size = len(queue)
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for start_index in range(size):
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start_node = queue[start_index]
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result.append(start_node)
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for end_node in digraph[start_node]:
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in_degree[end_node] -= 1
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if in_degree[end_node] == 0:
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queue.append(end_node)
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queue = queue[size:]
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# 判断是否可习完
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if len(result) == numCourses:
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return result
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return []
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if __name__ == "__main__":
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ans = Solution().findOrder(numCourses=2, prerequisites=[[1, 0]])
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assert sorted(ans) == sorted([0, 1])
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ans = Solution().findOrder(numCourses=4, prerequisites=[[1, 0], [2, 0], [3, 1], [3, 2]])
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assert sorted(ans) == sorted([0, 2, 1, 3])
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ans = Solution().findOrder(numCourses=1, prerequisites=[])
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assert sorted(ans) == sorted([0])
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ans = Solution().findOrder(numCourses=2, prerequisites=[])
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assert sorted(ans) == sorted([0, 1])

‎leetcode75/day26_815.py

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from collections import defaultdict
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from typing import List
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class Solution:
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def numBusesToDestination(self, routes: List[List[int]], source: int, target: int) -> int:
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# 不需要乘坐公交车,步行省钱还锻炼身体
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if source == target:
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return 0
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# 创建有向图
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bus = len(routes)
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visit = [False for _ in routes]
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edges = defaultdict(list)
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starts, ends = [], []
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for i in range(bus):
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# 寻找起始点,终点所在的公交线路
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if source in routes[i]:
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starts.append(i)
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visit[i] = True
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if target in routes[i]:
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ends.append(i)
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# 构建有向图
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for j in range(i + 1, bus):
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if set(routes[i]) & set(routes[j]):
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edges[i].append(j)
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edges[j].append(i)
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steps = 1
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if any(target in routes[start] for start in starts):
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return steps
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# 广度优先搜索
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while starts:
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size = len(starts)
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for index in range(size):
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cur_route = starts[index]
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for next_route in edges[cur_route]:
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if next_route in ends:
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return steps + 1
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elif visit[next_route] is False:
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starts.append(next_route)
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visit[next_route] = True
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starts = starts[size:]
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steps += 1
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return -1
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if __name__ == "__main__":
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assert Solution().numBusesToDestination(routes=[[1, 2, 7], [3, 6, 7]], source=1, target=6) == 2
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assert (
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Solution().numBusesToDestination(
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routes=[[7, 12], [4, 5, 15], [6], [15, 19], [9, 12, 13]], source=15, target=12
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)
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== -1
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)
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assert Solution().numBusesToDestination(routes=[[2], [2, 8]], source=8, target=2) == 1
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assert Solution().numBusesToDestination(routes=[[2], [2, 8]], source=8, target=8) == 0

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