354. Russian Doll Envelopes

You have a number of envelopes with widths and heights given as a pair of integers (w, h). One envelope can fit into another if and only if both the width and height of one envelope is greater than the width and height of the other envelope.What is the maximum number of envelopes can you Russian doll? (put one inside other)Example:Given envelopes = [[5,4],[6,4],[6,7],[2,3]], the maximum number of envelopes you can Russian doll is 3 ([2,3] => [5,4] => [6,7]).

• 这道题目比较简单，关键在于排序，排序完成后，本题就变得非常简单的动态规划。

class Solution {public:    static bool cmp(pair<int, int> a,pair<int, int> b){        if(a.first < b.first){            return true;        }        else if(a.first == b.first){            if(a.second < b.second){                return true;            }else{                return false;            }        }        else             return false;    }    int maxEnvelopes(vector<pair<int, int>>& envelopes) {        int n = envelopes.size();        sort(envelopes.begin(),envelopes.end(),cmp);           vector<int> dp(n,1);        int maxCnt = 1;        if(n <= 1){            return n;        }        dp[0] = 1;                for(int i = 1;i < n;++i){            for(int j = 0;j<i;++j){               if(envelopes[i].first > envelopes[j].first &&                  envelopes[i].second > envelopes[j].second){                    dp[i] = max(dp[i],dp[j]+1);                    maxCnt = max(maxCnt,dp[i]);               }             }        }        return maxCnt;    }};