JZ-064 - Maximum value of sliding window

Maximum value of sliding window

Topic description

Given an array and the size of the sliding window, find the maximum value of all values in the sliding window. For example, if the input array is {2,3,4,2,6,2,5,1} and the size of the sliding window is 3, then there are 6 sliding windows in total, and their maximum values are {4,4,6, 6,6,5}; There are six sliding windows for the array {2,3,4,2,6,2,5,1}: {[2,3,4],2,6,2,5 ,1}, {2,[3,4,2],6,2,5,1}, {2,3,[4,2,6],2,5,1}, {2,3,4 ,[2,6,2],5,1}, {2,3,4,2,[6,2,5],1}, {2,3,4,2,6,[2,5, 1]}.

• When the window is larger than the length of the array, return null.

topic link : maximum value of sliding window

code

import java.util.ArrayList;
import java.util.PriorityQueue;

/**
 * 标题：滑动窗口的最大值
 * 题目描述
 * 给定一个数组和滑动窗口的大小，找出所有滑动窗口里数值的最大值。例如，如果输入数组{2,3,4,2,6,2,5,1}及滑动窗口的大小3，那么一共存在6个滑动窗口，
 * 他们的最大值分别为{4,4,6,6,6,5}； 针对数组{2,3,4,2,6,2,5,1}的滑动窗口有以下6个： {[2,3,4],2,6,2,5,1}， {2,[3,4,2],6,2,5,1}，
 * {2,3,[4,2,6],2,5,1}， {2,3,4,[2,6,2],5,1}， {2,3,4,2,[6,2,5],1}， {2,3,4,2,6,[2,5,1]}。
 * 窗口大于数组长度的时候，返回空
 * 题目链接：
 * https://www.nowcoder.com/practice/1624bc35a45c42c0bc17d17fa0cba788?tpId=13&&tqId=11217&rp=1&ru=/ta/coding-interviews&qru=/ta/coding-interviews/question-ranking
 */
public class Jz64 {

    public ArrayList<Integer> maxInWindows(int[] num, int size) {
        ArrayList<Integer> result = new ArrayList<>();
        if (size > num.length || size < 1) {
            return result;
        }

        PriorityQueue<Integer> heap = new PriorityQueue<>((o1, o2) -> o2 - o1); // 大顶堆
        for (int i = 0; i < size; i++) {
            heap.add(num[i]);
        }
        result.add(heap.peek());
        for (int i = 0, j = i + size; j < num.length; i++, j++) { // 维护一个大小为 size 的大顶堆
            heap.remove(num[i]);
            heap.add(num[j]);
            result.add(heap.peek());
        }
        return result;
    }

    public static void main(String[] args) {
    
    }
}

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