986. Interval List Intersections

Given two lists of closed intervals, each list of intervals is pairwise disjoint and in sorted order.

Return the intersection of these two interval lists.

(Formally, 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 is either empty, or can be represented as a closed interval.  For example, the intersection of [1, 3] and [2, 4] is [2, 3].)

 

Example 1:

Input: A = [[0,2],[5,10],[13,23],[24,25]], B = [[1,5],[8,12],[15,24],[25,26]]
Output: [[1,2],[5,5],[8,10],[15,23],[24,24],[25,25]]
Reminder: The inputs and the desired output are lists of Interval objects, and not arrays or lists.

class Solution {
    public int[][] intervalIntersection(int[][] A, int[][] B) {
        if (A == null || A.length == 0 || B == null || B.length == 0) {
            return new int[0][0];
        }
        
        int m = A.length, n = B.length;
        int i = 0, j = 0;
        List<int[]> res = new ArrayList<>();
        while (i < m && j < n) {
            int[] a = A[i];
            int[] b = B[j];

            // find the overlap... if there is any...
            int startMax = Math.max(a[0], b[0]);
            int endMin = Math.min(a[1], b[1]);
            
            if (endMin >= startMax) {
                res.add(new int[]{startMax, endMin});
            }
            
            //update the pointer with smaller end value...
            if (a[1] == endMin) { i++; }
            if (b[1] == endMin) { j++; }
        }
        return res.toArray(new int[0][0]);
    }
}