# C++ recursive DP solution

• ``````bool compare(pair<int,int> &p1,pair<int,int> &p2){
return p1.first<p2.first;
}
class Solution {
public:
int maxEnvelopes(vector<pair<int, int>>& envelopes) {
int sz=envelopes.size();
if(sz<2)return sz;
sort(envelopes.begin(),envelopes.end(),compare);
envelopes.insert(envelopes.begin(),pair<int,int> (0,0));
sz++;
vector<int> table (sz,0);
return findDoll(envelopes,0,table)-1;
}

int findDoll(vector<pair<int,int>> &envelopes,int idx,vector<int> &table){
if(idx==envelopes.size()-1)return 1;
int maxDoll=0,doll;
for(int i=idx+1;i<envelopes.size();i++){
if(envelopes[i].first>envelopes[idx].first && envelopes[i].second>envelopes[idx].second){
doll=table[i]?table[i]:findDoll(envelopes,i,table);
maxDoll=max(maxDoll,doll);
}
}
maxDoll++;
table[idx]=maxDoll;
return maxDoll;
}
};
``````

By inserting a (0,0) envelope at the beginning of the sorted list, turn the question into recursively looking for the longest Russian doll start with the first element in the list.

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