LeetCode--841--medium--KeysAndRooms

summary:

graph | dfs 

package myapp.kit.leetcode.graph;

import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

/**
 *
 * 841
 * medium
 * https://leetcode.com/problems/keys-and-rooms/
 *
 * There are N rooms and you start in room 0.  Each room has a distinct number in 0, 1, 2, ..., N-1, and each room may have some keys to access the next room.
 *
 * Formally, each room i has a list of keys rooms[i], and each key rooms[i][j] is an integer in [0, 1, ..., N-1] where N = rooms.length.  A key rooms[i][j] = v opens the room with number v.
 *
 * Initially, all the rooms start locked (except for room 0).
 *
 * You can walk back and forth between rooms freely.
 *
 * Return true if and only if you can enter every room.
 *
 * Example 1:
 *
 * Input: [[1],[2],[3],[]]
 * Output: true
 * Explanation:
 * We start in room 0, and pick up key 1.
 * We then go to room 1, and pick up key 2.
 * We then go to room 2, and pick up key 3.
 * We then go to room 3.  Since we were able to go to every room, we return true.
 * Example 2:
 *
 * Input: [[1,3],[3,0,1],[2],[0]]
 * Output: false
 * Explanation: We can't enter the room with number 2.
 * Note:
 *
 * 1 <= rooms.length <= 1000
 * 0 <= rooms[i].length <= 1000
 * The number of keys in all rooms combined is at most 3000.
 *
 *
 * Created with IDEA
 * author:Dingsheng Huang
 * Date:2020/4/17
 * Time:下午9:06
 */
public class KeysAndRooms {

    private static int NODE_COLOR_WHITE = 0;
    private static int NODE_COLOR_BLACK = 1;

    Map<Integer, Integer> color = new HashMap<>();
    List<List<Integer>> graph = new ArrayList<>();

    public boolean canVisitAllRooms(List<List<Integer>> rooms) {
        // color init
        for (int i = 0; i < rooms.size(); i++) {
            color.put(i, NODE_COLOR_WHITE);
        }
        // graph init
        graph = rooms;
        dfs(0);
        return !color.containsValue(NODE_COLOR_WHITE);
    }

    private void dfs(Integer node) {
        if (color.get(node) == NODE_COLOR_BLACK) {
            return;
        }
        color.put(node, NODE_COLOR_BLACK);
        for (Integer neighbor : graph.get(node)) {
            dfs(neighbor);
        }
    }

}