34. Interval List Intersections

You are given two lists of closed intervals, firstList and secondList, where firstList[i] = [starti, endi] and secondList[j] = [startj, endj]. Each list of intervals is pairwise disjoint and in sorted order.

Return the intersection of these two interval lists.

A closed interval [a, b] (with a < b) denotes the set of real numbers x with a <= x <= b.

The intersection of two closed intervals is a set of real numbers that are either empty or represented as a closed interval. For example, the intersection of [1, 3] and [2, 4] is [2, 3].

Example 1:

Input: firstList = [[0,2],[5,10],[13,23],[24,25]], secondList = [[1,5],[8,12],[15,24],[25,26]]
Output: [[1,2],[5,5],[8,10],[15,23],[24,24],[25,25]]

Example 2:

Input: firstList = [[1,3],[5,9]], secondList = []
Output: []

Example 3:

Input: firstList = [], secondList = [[4,8],[10,12]]
Output: []

Example 4:

Input: firstList = [[1,7]], secondList = [[3,10]]
Output: [[3,7]]

Solution:

class Solution
{
public:
    vector<vector<int>> intervalIntersection(vector<vector<int>> &f, vector<vector<int>> &s)
    {
        vector<vector<int>> res;

        for (int i = 0; i < f.size(); i++)
        {
            for (int j = 0; j < s.size(); j++)
            {
                if (f[i][1] >= s[j][0])
                {
                    int start = max(f[i][0], s[j][0]);
                    int end = min(f[i][1], s[j][1]);
                    
                    if(start>end){
                        continue;
                    }
                    res.push_back({start, end});
                }
            }
        }
        return res;
    }
};