LeetCode:区间相关题目

class Solution {
public:
    vector<vector<int>> merge(vector<vector<int>>& intervals) {
        vector<vector<int>> ret;
        if (intervals.empty())
            return ret;
        sort(intervals.begin(), intervals.end(), [](vector<int>& a, vector<int>& b){return a[0] < b[0];});
        
        int i = 0;
        while (i < intervals.size()) {
            int beg = intervals[i][0];
            int end = intervals[i][1];
            ++i;
            while (i < intervals.size() && intervals[i][0] <= end) {
                end = max(end, intervals[i][1]);
                ++i;
            }
            ret.push_back(vector<int>{beg, end});
        }
        return ret;
    }
};

class Solution {
public:
    int eraseOverlapIntervals(vector<vector<int>>& intervals) {
        sort(intervals.begin(), intervals.end(), comp);
        int ret = 0;
        int pre = 0;
        for(int i = 1; i < intervals.size(); ++i) {
            if (intervals[i][0] < intervals[pre][1]) {
                ret++;
                if (intervals[i][1] < intervals[pre][1])
                    pre = i;
            }
            else
                pre = i;
        }
        return ret;
    }
private:
    static bool comp(vector<int>& a, vector<int>& b) {
        return a[0] < b[0];
    }
};

class Solution {
public:
    int findMinArrowShots(vector<vector<int>>& points) {
        sort(points.begin(), points.end(), comp);
        int ret = 0;
        int i = 0;
        while (i < points.size()) {
            int place = points[i][1];
            ++i;
            while (i < points.size() && points[i][0] <= place) {
                place = min(place, points[i][1]); 
                ++i;
            }
            ++ret;
        }
        return ret;
    }
private:
    static bool comp(vector<int>& a, vector<int>& b) {
        if (a[0] != b[0])
            return a[0] < b[0];
        else 
            return a[1] < b[1];
    }
};