Leetcode 547

Self improvement is procrastination, and self destruction.

547. Friend Circles

https://leetcode.com/problems/friend-circles/description/

思路: Graph DFS

原始方法:

class Solution547(object):

    def findCircleNum(self, M):

        """

        :type M: List[List[int]]

        :rtype: int

        """

        Circles = [];



        persons=set(range(0,len(M)))

        while persons:

            idx_start = list(persons)[0]

            circle = set()

            circle= self.dfs(M,idx_start,circle)

            Circles.append(list(circle))

            persons = persons.difference(circle)

        TotalCircles = len(Circles)

        return TotalCircles

    def dfs(self,M,i,circle):

        circle.add(i)

        idx_friends=self.findNewFriends(M[i],1,circle)

        for idx in idx_friends:

            circle =self.dfs(M,idx,circle)

        return circle



    def findNewFriends(self,array,target,Visited):

        #returns indices where the array elements are equal to target val

        idx_find = [];

        for idx,val in enumerate(array):

            if val == target and idx not in Visited:

                idx_find.append(idx);

        return idx_find

改进思路：原题不需要输出到底有哪些朋友圈路径，所以不必存储circle这个信息。直接在遍历的时候更改图M矩阵的值，运算速度会更快。