Interval List Intersections

Problem statement

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

My solution

/**
 * @param {number[][]} firstList
 * @param {number[][]} secondList
 * @return {number[][]}
 */
var intervalIntersection = function(firstList, secondList) {
    let i = 0;
    let j = 0;
    let result = [];
    
    while(i < firstList.length && j < secondList.length) {
        let firstItem = firstList[i];
        let secondItem = secondList[j];
        
        let doesIntersect = false;
        
        if (firstItem[1] < secondItem[1]) {
            if (firstItem[1] >= secondItem[0]) {
                doesIntersect = true
            }
            
            i++ 
        } else {
            if (secondItem[1] >= firstItem[0]) {
                doesIntersect = true
            }
            j++
        }
        
        if (doesIntersect) {
            result.push(
                [
                    Math.max(firstItem[0], secondItem[0]),
                    Math.min(firstItem[1], secondItem[1])
                ]
            )
            
        }
    }
    
    return result;
};