<p>You are given a 2D array of integers <code>envelopes</code> where <code>envelopes[i] = [w<sub>i</sub>, h<sub>i</sub>]</code> represents the width and the height of an envelope.</p>

<p>One envelope can fit into another if and only if both the width and height of one envelope are greater than the other envelope&#39;s width and height.</p>

<p>Return <em>the maximum number of envelopes you can Russian doll (i.e., put one inside the other)</em>.</p>

<p><strong>Note:</strong> You cannot rotate an envelope.</p>

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

<pre>
<strong>Input:</strong> envelopes = [[5,4],[6,4],[6,7],[2,3]]
<strong>Output:</strong> 3
<strong>Explanation:</strong> The maximum number of envelopes you can Russian doll is <code>3</code> ([2,3] =&gt; [5,4] =&gt; [6,7]).
</pre>

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

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

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

<ul>
	<li><code>1 &lt;= envelopes.length &lt;= 10<sup>5</sup></code></li>
	<li><code>envelopes[i].length == 2</code></li>
	<li><code>1 &lt;= w<sub>i</sub>, h<sub>i</sub> &lt;= 10<sup>5</sup></code></li>
</ul>

class Solution {
public:
    static bool cmp(vector<int>&v1,vector<int>&v2){
        if(v1[0]==v2[0]){
            return v1[1]>v2[1];
        }
        return v1[0]<v2[0];
    }
    int maxEnvelopes(vector<vector<int>>&nums) {
        int n=nums.size();
        sort(nums.begin(),nums.end(),cmp);
        vector<int> v;
        for(int i=0;i<n;i++){
            v.push_back(nums[i][1]);
        }
        set<int> s;
        for(int i=0;i<n;i++){
            auto it=s.lower_bound(v[i]);
            if(it!=s.end()){
                s.erase(it);
            }
            s.insert(v[i]);
        }
        return s.size();
    }
};
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