<p>Given an array&nbsp;of <code>intervals</code>&nbsp;where <code>intervals[i] = [start<sub>i</sub>, end<sub>i</sub>]</code>, merge all overlapping intervals, and return <em>an array of the non-overlapping intervals that cover all the intervals in the input</em>.</p>

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

<pre>
<strong>Input:</strong> intervals = [[1,3],[2,6],[8,10],[15,18]]
<strong>Output:</strong> [[1,6],[8,10],[15,18]]
<strong>Explanation:</strong> Since intervals [1,3] and [2,6] overlap, merge them into [1,6].
</pre>

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

<pre>
<strong>Input:</strong> intervals = [[1,4],[4,5]]
<strong>Output:</strong> [[1,5]]
<strong>Explanation:</strong> Intervals [1,4] and [4,5] are considered overlapping.
</pre>

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

<ul>
	<li><code>1 &lt;= intervals.length &lt;= 10<sup>4</sup></code></li>
	<li><code>intervals[i].length == 2</code></li>
	<li><code>0 &lt;= start<sub>i</sub> &lt;= end<sub>i</sub> &lt;= 10<sup>4</sup></code></li>
</ul>

class Solution {
public:
    static bool compare(vector<int> &a, vector<int> &b){
        return a[0] < b[0];
    }
    vector<vector<int>> merge(vector<vector<int>>& intervals) {
        sort(intervals.begin(), intervals.end(), compare);
        stack<pair<int,int>> st;

        st.push({intervals[0][0], intervals[0][1]});

        for(int i = 1; i < intervals.size(); i++){
            pair<int, int> p1 = st.top();
            pair<int, int> p2 = {intervals[i][0], intervals[i][1]};
            

            if(p2.first <= p1.second){
                st.pop();
                if(p2.second >= p1.second){
                    st.push({p1.first, p2.second});
                }
                else{
                    st.push({p1.first, p1.second});
                }
            }
            else{
                st.push({p2.first, p2.second});
            }
        }

        intervals.clear();

        while (!st.empty())
        {
            pair<int,int> val = st.top();
            intervals.push_back({val.first, val.second});
            st.pop();
        }
        return intervals;
    }
};
23400