标签：1042 Flower Planting garden paths int graph color flower
原题链接在这里：https://leetcode.com/problems/flower-planting-with-no-adjacent/
题目：
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]
Note:
1 <= N <= 100000 <= paths.size <= 20000- No garden has 4 or more paths coming into or leaving it.
- It is guaranteed an answer exists.
题解：
Build the graph with edges.
For one node, we could check for all its neighbors, what colors have been used. Have a color array to record which color has been used among its neighbors.
Then for this node color, it could choose one color that hasn't been used.
Time Compleixty: O(e + N). e = paths.length.
Space: O(e + N).
AC Java:
1 class Solution {
2 public int[] gardenNoAdj(int N, int[][] paths) {
3 Map<Integer, Set<Integer>> graph = new HashMap<>();
4 for(int i = 0; i < N; i++){
5 graph.put(i, new HashSet<Integer>());
6 }
7
8 for(int [] p : paths){
9 int x = p[0] - 1;
10 int y = p[1] - 1;
11 graph.get(x).add(y);
12 graph.get(y).add(x);
13 }
14
15 int [] res = new int[N];
16 for(int i = 0; i < N; i++){
17 int [] color = new int[5];
18 for(int nei : graph.get(i)){
19 color[res[nei]] = 1;
20 }
21
22 for(int c = 4; c >= 1; c--){
23 if(color[c] != 1){
24 res[i] = c;
25 }
26 }
27 }
28
29 return res;
30 }
31 }
标签：1042,Flower,Planting,garden,paths,int,graph,color,flower 来源： https://www.cnblogs.com/Dylan-Java-NYC/p/12539050.html
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