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1042. 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]

Note:

• 1 <= N <= 10000
• 0 <= paths.size <= 20000
• No garden has 4 or more paths coming into or leaving it.
• It is guaranteed an answer exists.

Solutions (Rust)

1. Solution

impl Solution {
    pub fn garden_no_adj(n: i32, paths: Vec<Vec<i32>>) -> Vec<i32> {
        let mut answer = vec![0; n as usize];
        let mut graph = vec![Vec::new(); n as usize];

        for path in paths {
            graph[path[0] as usize - 1].push(path[1] as usize - 1);
            graph[path[1] as usize - 1].push(path[0] as usize - 1);
        }

        for i in 0..answer.len() {
            let mut choice = 0;
            for &neighbor in &graph[i] {
                if neighbor < i {
                    choice |= 1 << (answer[neighbor] - 1);
                }
            }

            match choice {
                7 => answer[i] = 4,
                3|11 => answer[i] = 3,
                1|5|9|13 => answer[i] = 2,
                _ => answer[i] = 1,
            };
        }

        answer
    }
}