986. Interval List Intersections

https://leetcode.com/problems/interval-list-intersections/description/

给定各自没有overlap且排好序的两组intervals，找出它俩之间的交集。类似merge sort，两个指针指向当前的Intervals，看它俩有没有交集，即检查最小的end和最大的start是否有交叉。检查后移动end小的指针往前走。

/*
 * @lc app=leetcode id=986 lang=cpp
 *
 * [986] Interval List Intersections
 */

// @lc code=start
class Solution {
public:
    vector<vector<int>> intervalIntersection(vector<vector<int>>& A, vector<vector<int>>& B) {
        const int M = A.size(), N = B.size();
        int i = 0, j = 0;
        vector<vector<int>> res;
        while (i < M && j < N) {
            const auto &a = A[i], &b = B[j];
            const int s = max(a[0], b[0]), e = min(a[1], b[1]);
            if (s <= e) {
                res.push_back({s, e});
            }
            if (a[1] < b[1]) ++i;
            else ++j;
        }
        return res; 
    }
};
// @lc code=end