841.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.
解题思路d
可以将问题化简为一个有向图，如果这个图从0节点开始，可以遍历所有的节点，则返回true，否则返回发false。
代码如下：
class Solution {
public:
bool canVisitAllRooms(vector<vector<int>>& rooms) {
int NumOfVisited = 0;
vector<bool> visited(rooms.size());
stack<int> keystack;
keystack.push(0);
NumOfVisited++;
visited[0] = true;
while(!keystack.empty()) {
int room = keystack.top();
for (auto key : rooms[room]){
if (!visited[key]){
keystack.push(key);
visited[key] = true;
NumOfVisited++;
if (NumOfVisited == rooms.size())
return true;
}
}
}
return NumOfVisited == rooms.size();
}
};