Maximum Number of Events That Can Be Attended

Problem statement

You are 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. 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: 3Explanation: 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

Constraints:

• 1 <= events.length <= 105
• events[i].length == 2
• 1 <= startDayi <= endDayi <= 105

My solution

function maxEvents(events: number[][]): number {
    let result = 0;
    events.sort((a,b) => a[1]-b[1])
    let tree = new SegmentTree(1, events[events.length - 1][1], 1)
    for(let event of events) {
        const res = tree.query(event[0], event[1])
        if(res <= events[events.length - 1][1]) {
            result++
            tree.update(res, Number.MAX_SAFE_INTEGER)
        }
    }
    return result
};

class SegmentTree {
    start: number
    end: number
    left: SegmentTree 
    right: SegmentTree
    min: number
    
    constructor(s: number, e: number, m: number) {
        this.start = s
        this.end = e
        this.min = m
    }
    
    query(s: number, e: number): number {
        if (s > this.end || e < this.start) {
            return Number.MAX_SAFE_INTEGER
        }
        
        if (s <= this.start && e >= this.end) {
            return this.min
        }
        
        this.down()
        
        return Math.min(this.left.query(s,e), this.right.query(s,e))
    }
    
    update(pos: number, val: number) {
        if (pos > this.end || pos < this.start) {
            return
        }
        
        if(this.start == this.end) {
            this.min = val
            return
        }
        const middle = this.start + Math.floor((this.end - this.start) / 2)
        this.down()
        if (pos <= middle) {
            this.left.update(pos, val)
        } else {
            this.right.update(pos, val)
        }
        
        this.min = Math.min(this.left.min, this.right.min)
    }
    
    down() {
        if(this.start != this.end) {
            if(!this.left || !this.right) {
                const middle = this.start + Math.floor((this.end - this.start) / 2)
                this.left = new SegmentTree(this.start, middle, this.start)
                this.right = new SegmentTree(middle + 1, this.end, middle + 1)
            }
        }
    }
    
}