56 合并区间

https://leetcode.cn/leetbook/read/top-interview-questions-medium/xv11yj/

cost: 13m49s

class Solution {
public:
    vector<vector<int>> merge(vector<vector<int>>& intervals) {
        std::sort(intervals.begin(), intervals.end(),
                  [](vector<int> a, vector<int> b) { return a[0] < b[0]; });
        vector<vector<int>> res;
        for (const auto interval : intervals) {
            if (res.empty()) {
                res.push_back(interval);
                continue;
            }
            auto& back = res.back();
            if (back[1] < interval[0]) {
                res.push_back(interval);
            } else {
                back[1] = std::max(interval[1], back[1]);
            }
        }
        return res;
    }
};