Package g1901_2000.s1916_count_ways_to_build_rooms_in_an_ant_colony

Class Solution

java.lang.Object

g1901_2000.s1916_count_ways_to_build_rooms_in_an_ant_colony.Solution

public class Solution
extends Object

1916 - Count Ways to Build Rooms in an Ant Colony\. Hard You are an ant tasked with adding `n` new rooms numbered `0` to `n-1` to your colony. You are given the expansion plan as a **0-indexed** integer array of length `n`, `prevRoom`, where `prevRoom[i]` indicates that you must build room `prevRoom[i]` before building room `i`, and these two rooms must be connected **directly**. Room `0` is already built, so `prevRoom[0] = -1`. The expansion plan is given such that once all the rooms are built, every room will be reachable from room `0`. You can only build **one room** at a time, and you can travel freely between rooms you have **already built** only if they are **connected**. You can choose to build **any room** as long as its **previous room** is already built. Return _the **number of different orders** you can build all the rooms in_. Since the answer may be large, return it **modulo** 109 + 7. **Example 1:**  **Input:** prevRoom = [-1,0,1] **Output:** 1 **Explanation:** There is only one way to build the additional rooms: 0 → 1 → 2 **Example 2:** **** **Input:** prevRoom = [-1,0,0,1,2] **Output:** 6 **Explanation:** The 6 ways are: 0 → 1 → 3 → 2 → 4 0 → 2 → 4 → 1 → 3 0 → 1 → 2 → 3 → 4 0 → 1 → 2 → 4 → 3 0 → 2 → 1 → 3 → 4 0 → 2 → 1 → 4 → 3 **Constraints:** * `n == prevRoom.length` * 2 <= n <= 105 * `prevRoom[0] == -1` * `0 <= prevRoom[i] < n` for all `1 <= i < n` * Every room is reachable from room `0` once all the rooms are built.

Constructor Summary

Constructors

Constructor	Description
Solution()

Method Summary

Modifier and Type	Method	Description
int	waysToBuildRooms(int[] prevRoom)

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Details

Solution

public Solution()

Method Details

waysToBuildRooms

public int waysToBuildRooms(int[] prevRoom)