Today I have done leetcode's May LeetCoding Challenge with cpp.

May LeetCoding Challenge 25

Description

Russian Doll Envelopes

You are given a 2D array of integers envelopes where envelopes[i] = [wi, hi] represents the width and the height of an envelope.

One envelope can fit into another if and only if both the width and height of one envelope are greater than the other envelope's width and height.

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

Note: You cannot rotate an envelope.

Example 1:

Input: envelopes = [[5,4],[6,4],[6,7],[2,3]]
Output: 3
Explanation: The maximum number of envelopes you can Russian doll is 3 ([2,3] => [5,4] => [6,7]).

Example 2:

Input: envelopes = [[1,1],[1,1],[1,1]]
Output: 1

Constraints:

• 1 <= envelopes.length <= 105
• envelopes[i].length == 2
• 1 <= wi, hi <= 105

Solution

class Solution {
public:
  int maxEnvelopes(vector<vector<int>>& envelopes) {
    sort(envelopes.begin(), envelopes.end(), [](vector<int> &a, vector<int> &b){
      return a[0] < b[0] || (a[0] == b[0] && a[1] > b[1]);
    });
    vector<int> dp;
    for(auto &e : envelopes) {
      auto it = lower_bound(dp.begin(), dp.end(), e[1]);
      if(it == dp.end()) {
        dp.push_back(e[1]);
      } else {
        *it = e[1];
      }
    }
    return dp.size();
  }
};

// Accepted
// 231/231 cases passed (4 ms)
// Your runtime beats 73.76 % of cpp submissions
// Your memory usage beats 96.04 % of cpp submissions (6.7 MB)