986. Interval List Intersections

Description

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].

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

Approach

Links

• GeeksforGeeks

• Leetcode

• ProgramCreek

• YouTube

Examples

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]]

Solutions

Solution 1

/**
 * Time complexity : O(M+N), where M, N are the lengths of A and B respectively.
 * Space complexity : O(M+N), the maximum size of the answer.
 */

class Solution {
    public int[][] intervalIntersection(int[][] firstList, int[][] secondList) {
        List<int[]> resultList = new ArrayList<int[]>();
        
        int m = firstList.length, n = secondList.length, i = 0, j = 0;
        
        while(i < m && j < n) {
            int low = Math.max(firstList[i][0], secondList[j][0]);
            int high = Math.min(firstList[i][1], secondList[j][1]);
            
            if(low <= high) {
                resultList.add(new int[]{low, high});
            }
            
            if(firstList[i][1] < secondList[j][1]) {
                i++;
            } else {
                j++;
            }
        }
        
        return resultList.toArray(new int[resultList.size()][2]);
    }
}

Follow up