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);
}
}
}