Lintcode 127. Topological Sorting (Medium) Python

最新推荐文章于 2022-06-01 13:11:23 发布

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本文详细介绍了如何使用拓扑排序算法解决有向无环图的排序问题。通过统计节点的入度，将入度为0的节点加入队列，再进行广度优先搜索，最终实现对图中节点的正确排序。

题目：https://www.lintcode.com/problem/topological-sorting/description
思路：拓扑排序
1.统计所有点的入度
2.将入度为0的加入队列
3.bfs

"""
Definition for a Directed graph node
class DirectedGraphNode:
    def __init__(self, x):
        self.label = x
        self.neighbors = []    # 存的是DirectedGraphNode
# len(graph) 得到node的个数
"""

class Solution:
    """
    @param: graph: A list of Directed graph node
    @return: Any topological order for the given graph.
    """
    def topSort(self, graph):
        # write your code here
        if graph == None :
            return []
        
        indegree = self.indegreehelper(graph)
        queue = [] 
        for i in range(len(graph)):
            if indegree[i][0] == 0:
                 queue.append(graph[i])
        result = []
        hashtable = set()
        while queue :
            current = queue.pop(0)
            result.append(current)
            for i in indegree[current.label][1]:
                indegree[i.label][0] -= 1
                if indegree[i.label][0] == 0:
                    queue.append(graph[i.label])
        return result
        
    def indegreehelper(self,graph):
        indegree = [[0,[]] for x in range(len(graph))]
        print indegree
        for i in range(len(graph)):
            for j in graph[i].neighbors:
                indegree[j.label][0] += 1
            indegree[i][1] = graph[i].neighbors
        return indegree