LeetCode 1997: First Day Where You Have Been in All the Rooms Solution

Master LeetCode problem 1997 (First Day Where You Have Been in All the Rooms), a medium challenge, with our optimized solutions in Java, C++, and Python. Explore detailed explanations, test your code in our interactive editor, and prepare for coding interviews.

1997. First Day Where You Have Been in All the Rooms

Medium

Array Dynamic Programming

Problem Explanation

Explanation:

To solve this problem, we need to simulate the process of visiting rooms on each day based on the given rules until we have visited all the rooms. We keep track of the number of times each room has been visited and the current day. We iterate through the days, updating the room to be visited next based on whether the current room has been visited an odd or even number of times.

Algorithm:

Initialize variables: n as the number of rooms, days as the current day, visited array to keep track of visits to each room, and mod as 10^9 + 7.
Start visiting rooms from day 0, update the number of visits for each room, and determine the next room to visit based on the rules.
Continue visiting rooms until all rooms have been visited.
Return the first day where all rooms have been visited modulo mod.

Time Complexity:

The time complexity of this algorithm is O(n) where n is the number of rooms.

Space Complexity:

The space complexity of this algorithm is O(n) for the visited array.

Solution Code

class Solution {
    public int firstDayBeenInAllRooms(int[] nextVisit) {
        int n = nextVisit.length;
        int mod = 1000000007;
        int[] visited = new int[n];
        long days = 0;
        
        for (int i = 0; i < n; i++) {
            days = (days + nextVisit[i] + 1) % mod;
        }
        
        for (int i = 0; i < n - 1; i++) {
            visited[i + 1] = (int)((visited[i] + 2 + mod - nextVisit[i] - days + mod) % mod);
            days = (days + visited[i] + 2) % mod;
        }
        
        return (int)days;
    }
}

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