Interval_List_Intersections.java

/*

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: []
 

Constraints:

0 <= firstList.length, secondList.length <= 1000
firstList.length + secondList.length >= 1
0 <= starti < endi <= 109
endi < starti+1
0 <= startj < endj <= 109 
endj < startj+1

*/
import java.util.*;
class Inteval_List_Intersections {
    public int[][] intervalIntersection(int[][] firstList, int[][] secondList) {
        List<int[]> ans = new ArrayList<>();
        int n = firstList.length;
        int m = secondList.length;
        int i = 0;
        int j = 0;

        while (i < n && j < m) {
            int start1 = firstList[i][0];
            int end1 = firstList[i][1];
            int start2 = secondList[j][0];
            int end2 = secondList[j][1];

            if (start1 <= start2) {
                if (end1 >= start2) {
                    int s = Math.max(start1, start2);
                    int e = Math.min(end1, end2);
                    ans.add(new int[]{s, e});
                }
            } else if (end2 >= start1) {   
                int s = Math.max(start1, start2);
                int e = Math.min(end1, end2);
                ans.add(new int[]{s, e});
            }

            if (end1 < end2) {
                i++;
            } else {
                j++;
            }
        }

        return ans.toArray(new int[ans.size()][]);
    }
}