<p>There are <code>n</code> different online courses numbered from <code>1</code> to <code>n</code>. You are given an array <code>courses</code> where <code>courses[i] = [duration<sub>i</sub>, lastDay<sub>i</sub>]</code> indicate that the <code>i<sup>th</sup></code> course should be taken <b>continuously</b> for <code>duration<sub>i</sub></code> days and must be finished before or on <code>lastDay<sub>i</sub></code>.</p>

<p>You will start on the <code>1<sup>st</sup></code> day and you cannot take two or more courses simultaneously.</p>

<p>Return <em>the maximum number of courses that you can take</em>.</p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>

<pre>
<strong>Input:</strong> courses = [[100,200],[200,1300],[1000,1250],[2000,3200]]
<strong>Output:</strong> 3
Explanation: 
There are totally 4 courses, but you can take 3 courses at most:
First, take the 1<sup>st</sup> course, it costs 100 days so you will finish it on the 100<sup>th</sup> day, and ready to take the next course on the 101<sup>st</sup> day.
Second, take the 3<sup>rd</sup> course, it costs 1000 days so you will finish it on the 1100<sup>th</sup> day, and ready to take the next course on the 1101<sup>st</sup> day. 
Third, take the 2<sup>nd</sup> course, it costs 200 days so you will finish it on the 1300<sup>th</sup> day. 
The 4<sup>th</sup> course cannot be taken now, since you will finish it on the 3300<sup>th</sup> day, which exceeds the closed date.
</pre>

<p><strong class="example">Example 2:</strong></p>

<pre>
<strong>Input:</strong> courses = [[1,2]]
<strong>Output:</strong> 1
</pre>

<p><strong class="example">Example 3:</strong></p>

<pre>
<strong>Input:</strong> courses = [[3,2],[4,3]]
<strong>Output:</strong> 0
</pre>

<p>&nbsp;</p>
<p><strong>Constraints:</strong></p>

<ul>
	<li><code>1 &lt;= courses.length &lt;= 10<sup>4</sup></code></li>
	<li><code>1 &lt;= duration<sub>i</sub>, lastDay<sub>i</sub> &lt;= 10<sup>4</sup></code></li>
</ul>

class Solution {
public:
    using int2 = pair<int,int> ;
    static bool cmpr(vector<int> a,vector<int>b ){
        return a[1]<b[1];
    }
    int scheduleCourse(vector<vector<int>>& c) {
        std::ios_base::sync_with_stdio(false);
        std::cout.tie(nullptr);
        std::cin.tie(nullptr);
        sort(c.begin(),c.end(), cmpr);
        priority_queue<int> pq;
        int n =c.size();
        int ans = 0,time = 0;
        for(int i=0; i<n; i++){
            time += c[i][0];
            pq.push(c[i][0]);
            if(time > c[i][1]){
                time -= pq.top();
                pq.pop();
            }
            ans = max(ans,(int)pq.size());
        }
        return ans;
    }
};
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