leetcode1042 Flower Planting With No Adjacent

"""
You have N gardens, labelled 1 to N.  In each garden, you want to plant one of 4 types of flowers.
paths[i] = [x, y] describes the existence of a bidirectional path from garden x to garden y.
Also, there is no garden that has more than 3 paths coming into or leaving it.
Your task is to choose a flower type for each garden such that, for any two gardens connected by a path, they have different types of flowers.
Return any such a choice as an array answer, where answer[i] is the type of flower planted in the (i+1)-th garden.  The flower types are denoted 1, 2, 3, or 4.  It is guaranteed an answer exists.
Example 1:
Input: N = 3, paths = [[1,2],[2,3],[3,1]]
Output: [1,2,3]
Example 2:
Input: N = 4, paths = [[1,2],[3,4]]
Output: [1,2,1,2]
Example 3:
Input: N = 4, paths = [[1,2],[2,3],[3,4],[4,1],[1,3],[2,4]]
Output: [1,2,3,4]
"""
"""
此题用贪心算法
没掌握
"""
class Solution(object):
    def gardenNoAdj(self, N, paths):
        res = [0] * N
        m = [[] for i in range(N + 1)]  # 用来存第i个结点到其他结点的路径，i为1到N
        for x, y in paths:
            m[x].append(y)
            m[y].append(x)
        for i in range(1, N + 1):  # 对N个路径进行遍历
            used = set()  # 用来存这个结点出现的所有路径使用过的颜色
            for j in m[i]:
                used.add(res[j - 1])  # 把目的地的颜色放入used里
            for j in range(1, 5):  # 1，2，3，4代表四种颜色
                if j not in used:
                    res[i - 1] = j  # 将该结点存入新的颜色
                    break
        return res