Leet Code 632. Smallest Range Covering Elements from K Lists

https://leetcode.com/problems/smallest-range-covering-elements-from-k-lists/

Example 1:

Input: nums = [[4,10,15,24,26],[0,9,12,20],[5,18,22,30]]
Output: [20,24]
Explanation: 
List 1: [4, 10, 15, 24,26], 24 is in range [20,24].
List 2: [0, 9, 12, 20], 20 is in range [20,24].
List 3: [5, 18, 22, 30], 22 is in range [20,24].

package pep.Day67;

import java.util.List;
import java.util.PriorityQueue;
import java.util.Queue;

public class LeetCode_632_Smallest_Range_Covering_Elements_from_K_Lists {

    public static class Pair implements Comparable<Pair> {
        int r, c, val;

        Pair(int r, int c, int val) {
            this.r = r;
            this.c = c;
            this.val = val;
        }

        public int compareTo(Pair other) {
            return this.val - other.val;
        }


    }

    public static int[] smallestRange(List<List<Integer>> nums) {

        Queue<Pair> pq = new PriorityQueue<>();
        int n = nums.size(), max = Integer.MIN_VALUE, range = Integer.MAX_VALUE, firstNumber = -1, secondNumber = -1;

        // sab list mese ek ek element queue me daal diya, also, max nikal liya
        for (int i = 0; i < n; i++) {
            pq.add(new Pair(i, 0, nums.get(i).get(0)));
            max = Math.max(max, nums.get(i).get(0));
        }

        while (pq.size() == n) {
            Pair rem = pq.remove();

            // update range agr choti mile to
            if (max - rem.val < range) {
                range = max - rem.val;
                firstNumber = rem.val;
                secondNumber = max;
            }

            if (rem.c + 1 < nums.get(rem.r).size()) {
                pq.add(new Pair(rem.r, rem.c + 1, nums.get(rem.r).get(rem.c + 1)));
                max = Math.max(max, nums.get(rem.r).get(rem.c + 1));
            }

        }

        return new int[]{firstNumber, secondNumber};

    }
}