Interval List Intersections

Problem Statement - link #

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].

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]]

Constraints #

• 0 <= firstList.length, secondList.length <= 1000
• firstList.length + secondList.length >= 1
• 0 <= starti < endi <= 10^9
• endi < starti+1
• 0 <= startj < endj <= 10^9
• endj < startj+1

Solutions #

class Solution {
public:
    vector<vector<int>> intervalIntersection(vector<vector<int>>& firstList, vector<vector<int>>& secondList) {
        
        vector<vector<int>> result;
        int itr1 = 0, itr2 = 0;
        
        while( itr1 < firstList.size() and itr2 < secondList.size()){
            
            int start = max(firstList[itr1][0], secondList[itr2][0]);            
            int end = min(firstList[itr1][1], secondList[itr2][1]);
            
            if(start <= end) result.push_back({start,end}) ;
            
            firstList[itr1][1] < secondList[itr2][1] ? itr1++ : itr2++ ; 
        }
        
        return result;
    }
};