差分数组

class Solution {
public:

    int minMeetingRooms(vector<vector<int>>& a) {
        int maxn = 0;

        for(auto& x:a){
            maxn = std::max<int>(maxn,x[0]);
            maxn = std::max<int>(maxn,x[1]);
        }
        maxn += 1;
        vector<int> s (maxn,0);
        for(auto& x:a){
            ++s [x[0]];
            -- s[x[1]];
        }
        int ret = s[0];
        for(int i=1;i<maxn;++i){
            s[i] += s[i-1];
            ret = max<int>(ret,s[i]);
        }
        return ret;
    }
};

会议起点和终点解耦

​​https://leetcode.cn/problems/meeting-rooms-ii/solution/hui-yi-shi-ii-by-leetcode/​​

class Solution {
public:

    int minMeetingRooms(vector<vector<int>>& a) {
        int n = a.size();
        vector<int> s(n,0);
        vector<int> e(n,0);

        for(int i=0;i<a.size();++i){
            s[i] = a[i][0];
            e[i] = a[i][1];
        }

        sort(s.begin(),s.end());
        sort(e.begin(),e.end());
        
        int ret = 1;
        int j=0;
        for(int i=1;i<n;++i){
            if( e[j] <= s[i]  ){
                ++j;
            }else{
                ++ret;
            }
        }
        return ret;
    }
};

【LeetCode】253. 会议室 II_算法