[LeetCode]632. Smallest Range

https://leetcode.com/problems/smallest-range/#/description

给k个递增数组，找出一个最小范围，保证每个数组内至少有一个数字落在这个区间上

类似归并排序思想——多维有序数组问题考虑mergeSort+pq思想

pq内每次poll出当前最小值，max保存当前已访问的最大值，当前pq中的所有值一定在这个区间内（满足该区间覆盖所有数组条件），只要看这个区间是否为更小的那个区间即可

public class Solution {    public int[] smallestRange(List<List<Integer>> nums) {        int start = -1;        int end = -1;        int max = Integer.MIN_VALUE;        int range = Integer.MAX_VALUE;        PriorityQueue<Element> queue = new PriorityQueue(new Comparator<Element>() {            public int compare(Element e1, Element e2) {                return e1.val - e2.val;            }        });        for (int i = 0; i < nums.size(); i++) {            Element e = new Element(nums.get(i).get(0), 0, i);            queue.offer(e);            max = Math.max(max, e.val);        }        while (queue.size() == nums.size()) {            Element e = queue.poll();            if (max - e.val < range) {                range = max - e.val;                start = e.val;                end = max;            }            if (e.index + 1 < nums.get(e.row).size()) {                e.index = e.index + 1;                e.val = nums.get(e.row).get(e.index);                queue.offer(e);                if (e.val > max) {                    max = e.val;                }            }        }        return new int[]{start, end};    }    class Element {        int index;        int row;        int val;        public Element(int val, int index, int row) {            this.val = val;            this.index = index;            this.row = row;        }    }}