leetcode题解 632. Smallest Range

版权声明：本文为博主原创文章，未经博主允许不得转载。 https://blog.csdn.net/ljyss9/article/details/74999666

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


题意：找到一个范围，可以存在n个list都有数在这个范围内

思路：类似于merge多个有序数组，用heap存储n个数，每个List一个，然后每次poll，找出最小的数，并安排该List加入新的元素，然后用max - min，找出范围，最后给出最小的范围，就是类似于归并排序中的merge函数，逐步合并，找出范围

public int[] smallestRange(int[][] nums) {
PriorityQueue<Element> pq = new PriorityQueue<Element>(new Comparator<Element>() {
public int compare(Element a, Element b) {
return a.val - b.val;
}
});
int min = Integer.MAX_VALUE, max = Integer.MIN_VALUE;
for (int i = 0; i < nums.length; i++) {
Element e = new Element(i, 0, nums[i][0]);
pq.offer(e);
max = Math.max(max, nums[i][0]);
}
int range = Integer.MAX_VALUE;
int start = -1, end = -1;
while (pq.size() == nums.length) {


Element curr = pq.poll();
if (max - curr.val < range) {
range = max - curr.val;
start = curr.val;
end = max;
}
if (curr.idx + 1 < nums[curr.row].length) {
curr.idx = curr.idx + 1;
curr.val = nums[curr.row][curr.idx];
pq.offer(curr);
if (curr.val > max) {
max = curr.val;
}
}
}


return new int[] { start, end };
}


class Element {
int val;
int idx;
int row;


public Element(int r, int i, int v) {
val = v;
idx = i;
row = r;
}
}