Interval List Intersections

Given two lists of closed intervals, each sorted and disjoint, return their intersection.

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]]

Solution Approach

Two pointers: at each step compute intersection of current intervals. Advance the pointer of the interval that ends first.

i=0 pointer for A, j=0 for B.
Intersection: [max(A[i][0], B[j][0]), min(A[i][1], B[j][1])].
If lo <= hi, add to result.
Advance whichever interval ends first (min end pointer).

Java

import java.util.*;

class Solution {
    public int[][] intervalIntersection(int[][] A, int[][] B) {
        List<int[]> res = new ArrayList<>();
        int i = 0, j = 0;
        while (i < A.length && j < B.length) {
            int lo = Math.max(A[i][0], B[j][0]);
            int hi = Math.min(A[i][1], B[j][1]);
            if (lo <= hi) res.add(new int[]{lo, hi});
            if (A[i][1] < B[j][1]) i++;
            else j++;
        }
        return res.toArray(new int[0][]);
    }
}

Time Complexity: O(M+N)
Space Complexity: O(M+N)