最小区间

/*
  思路：
  虽然Java Stream不适合处理此问题的所有步骤，但可以用于初始化列表和获取最小值最大值等辅助操作。
  我们将使用最小堆来解决主要问题。
*/
import java.util.*;
import java.util.stream.*;
 
public class SmallestRangeStream {
    public int[] smallestRange(List<List<Integer>> nums) {
        PriorityQueue<int[]> minHeap = new PriorityQueue<>(Comparator.comparingInt(a -> a[0]));
        int currentMax = nums.stream().mapToInt(list -> list.get(0)).max().orElse(Integer.MIN_VALUE);
 
        nums.stream().map(list -> new int[]{list.get(0), nums.indexOf(list), 0})
                .forEach(minHeap::offer);
 
        int minRange = Integer.MAX_VALUE;
        int start = -1;
        int end = -1;
 
        while (minHeap.size() == nums.size()) {
            int[] current = minHeap.poll();
            int currentMin = current[0];
            int listIndex = current[1];
            int elementIndex = current[2];
 
            if (currentMax - currentMin < minRange) {
                minRange = currentMax - currentMin;
                start = currentMin;
                end = currentMax;
            }
 
            if (elementIndex + 1 < nums.get(listIndex).size()) {
                int nextElement = nums.get(listIndex).get(elementIndex + 1);
                minHeap.offer(new int[]{nextElement, listIndex, elementIndex + 1});
                currentMax = Math.max(currentMax, nextElement);
            }
        }
 
        return new int[]{start, end};
    }
}