Introduction

In this blog post, we will explore how to solve the LeetCode problem "1997" using AI. LeetCode is a popular platform for preparing for coding interviews, and with the help of AI tools like Chatmagic, we can generate solutions quickly and efficiently - helping you pass the interviews and get the job offer without having to study for months.

Problem Statement

There are n rooms you need to visit, labeled from 0 to n - 1. Each day is labeled, starting from 0. You will go in and visit one room a day. Initially on day 0, you visit room 0. The order you visit the rooms for the coming days is determined by the following rules and a given 0-indexed array nextVisit of length n: Assuming that on a day, you visit room i, if you have been in room i an odd number of times (including the current visit), on the next day you will visit a room with a lower or equal room number specified by nextVisit[i] where 0 <= nextVisit[i] <= i; if you have been in room i an even number of times (including the current visit), on the next day you will visit room (i + 1) mod n. Return the label of the first day where you have been in all the rooms. It can be shown that such a day exists. Since the answer may be very large, return it modulo 109 + 7. Example 1: Input: nextVisit = [0,0] Output: 2 Explanation: - On day 0, you visit room 0. The total times you have been in room 0 is 1, which is odd. On the next day you will visit room nextVisit[0] = 0 - On day 1, you visit room 0, The total times you have been in room 0 is 2, which is even. On the next day you will visit room (0 + 1) mod 2 = 1 - On day 2, you visit room 1. This is the first day where you have been in all the rooms. Example 2: Input: nextVisit = [0,0,2] Output: 6 Explanation: Your room visiting order for each day is: [0,0,1,0,0,1,2,...]. Day 6 is the first day where you have been in all the rooms. Example 3: Input: nextVisit = [0,1,2,0] Output: 6 Explanation: Your room visiting order for each day is: [0,0,1,1,2,2,3,...]. Day 6 is the first day where you have been in all the rooms. Constraints: n == nextVisit.length 2 <= n <= 105 0 <= nextVisit[i] <= i

Explanation

Here's the breakdown of the solution:

• Simulate the process: Iterate through the days, keeping track of the current room and the number of times each room has been visited. Apply the given rules to determine the next room to visit.
• Modulo Arithmetic: Perform all calculations modulo 10⁹ + 7 to prevent integer overflow.

• Optimization: The simulation continues until all rooms have been visited at least once.

• Runtime Complexity: O(n k) where k is the number of days it takes to visit all rooms for the first time. In the worst case, it can approach O(n^2). *Storage Complexity: O(n)

Code

    def firstDayBeenInAllRooms(nextVisit):
    n = len(nextVisit)
    visits = [0] * n
    current_room = 0
    day = 0
    visited_all = False
    MOD = 10**9 + 7

    while not visited_all:
        visits[current_room] += 1

        visited_all = True
        for count in visits:
            if count == 0:
                visited_all = False
                break

        if visited_all:
            break

        if visits[current_room] % 2 == 1:
            current_room = nextVisit[current_room]
        else:
            current_room = (current_room + 1) % n

        day += 1

    return day % MOD