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Interval List Intersections

Created: March 16, 2020 by [lek-tin]

Last updated: April 23, 2020

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

interval list intersections 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.

Constraints

  1. 0 <= A.length < 1000
  2. 0 <= B.length < 1000
  3. 0 <= A[i].start, A[i].end, B[i].start, B[i].end < 10^9

NOTE: input types have been changed on April 15, 2019. Please reset to default code definition to get new method signature.

Solution

Java

class Solution {
    public int[][] intervalIntersection(int[][] A, int[][] B) {
        int i = 0, j = 0;
        ArrayList<int[]> res = new ArrayList<>();

        while (i < A.length && j < B.length) {
            int low  = Math.max(A[i][0], B[j][0]);
            int high = Math.min(A[i][1], B[j][1]);
            if (low <= high) {
                res.add(new int[]{low, high});
            }

            if (A[i][1] < B[j][1]) {
                i++;
            } else {
                j++;
            }
        }

        return res.toArray(new int[res.size()][2]);
    }
}

Python

class Solution:
    def intervalIntersection(self, A: List[List[int]], B: List[List[int]]) -> List[List[int]]:
        ans = []
        i = j = 0

        while i < len(A) and j < len(B):
            # Let's check if A[i] intersects B[j].
            # lo - the startpoint of the intersection
            # hi - the endpoint of the intersection
            lo = max(A[i][0], B[j][0])
            hi = min(A[i][1], B[j][1])
            if lo <= hi:
                ans.append([lo, hi])

            # Remove the interval with the smaller endpoint
            if A[i][1] < B[j][1]:
                i += 1
            else:
                j += 1

        return ans