LintCode 127. Topological Sorting

题目

思路

1.找到所有结点的入度
2.找到所有入度为0的结点。注意，这里有坑，入度为0的结点有可能不止有一个。
3.BFS

代码

"""
Definition for a Directed graph node
class DirectedGraphNode:
    def __init__(self, x):
        self.label = x
        self.neighbors = []
"""


class Solution:
    """
    @param: graph: A list of Directed graph node
    @return: Any topological order for the given graph.
    """
    def getInDegree(self, graph):
        inDegreeDict = {}
        queue = []
        for node in graph:
            for neighbor in node.neighbors:
                if neighbor in inDegreeDict:
                    inDegreeDict[neighbor] += 1
                else: inDegreeDict[neighbor] = 1
        return inDegreeDict
    def getStartNode(self, inDegreeDict, graph):
        startNodes = []
        for node in graph:
            if node and node not in inDegreeDict:
                startNodes.append(node)
        return startNodes
    def topSort(self, graph):
        # write your code here
        queue = []
        res_list = []
        if not graph:
            return []
        inDegreeDict = self.getInDegree(graph)
        startNodes = self.getStartNode(inDegreeDict, graph)
        for node in startNodes:
            queue.append(node)
        while queue:
            node = queue[0]
            queue.pop(0)
            res_list.append(node)
            for neighbor in node.neighbors:
                inDegreeDict[neighbor] -= 1
                if not inDegreeDict[neighbor]:
                    queue.append(neighbor)
        return res_list