1353. Maximum Number of Events That Can Be Attended.md

1353. Maximum Number of Events That Can Be Attended

Given an array of events where events[i] = [startDayi, endDayi]. Every event i starts at startDayi and ends at endDayi.

You can attend an event i at any day d where startTimei <= d <= endTimei. Notice that you can only attend one event at any time d.

Return the maximum number of events you can attend.

 
Example 1:


Input: events = [[1,2],[2,3],[3,4]]
Output: 3
Explanation: You can attend all the three events.
One way to attend them all is as shown.
Attend the first event on day 1.
Attend the second event on day 2.
Attend the third event on day 3.
Example 2:

Input: events= [[1,2],[2,3],[3,4],[1,2]]
Output: 4
Example 3:

Input: events = [[1,4],[4,4],[2,2],[3,4],[1,1]]
Output: 4
Example 4:

Input: events = [[1,100000]]
Output: 1
Example 5:

Input: events = [[1,1],[1,2],[1,3],[1,4],[1,5],[1,6],[1,7]]
Output: 7

Solution 1

• sort by end time and greedy
• it is helpful to have image in mind

class Solution {
    public int maxEvents(int[][] events) {
        //have the graph in my mind
        //sort by end time
        Arrays.sort(events, (a, b)-> a[1]-b[1]);
        boolean[] days = new boolean[100001]; //assume all false
        int res = 0;
        for(int i = 0; i<events.length; i++){
            for(int j = events[i][0]; j<=events[i][1]; j++){
                if(days[j]==true) continue;
                days[j] = true;
                res++;
                break;
            }
        }
        return res;
    }
}

Solution 2

• ??

Reference

• https://www.youtube.com/watch?v=NjF9JGDGxg8
• good image