Sword refers to Offer-61-the maximum value in the sliding window

Title description

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

Idea analysis

It is mainly solved by recursion and double pointers.

Code

import java.util.ArrayList;
public class Solution {
    
    
    ArrayList<Integer> list = new ArrayList<>();
    int len = -1;//窗口长度
    int start = 0;//开始处
    int end = 0;//结束处
    public ArrayList<Integer> maxInWindows(int [] num, int size)
    {
    
    
        
        if(num == null||num.length<size||size == 0){
    
    
            return list;
        }
        start = 0;//滑动窗口的开始
        end = size-1;//滑动窗口的结束
        len = size;
        maxInWindowsHelper(num,start,end);
        return list;
    }
    public void maxInWindowsHelper(int[] num,int start,int end){
    
    
        if(end<num.length){
    
    
            int max = -1;
            for(int i = start; i<=end;i++){
    
    
                //通过循环获得每一次的最大值
                if(num[i]>max){
    
    
                    max = num[i];
                }
            }
           list.add(max);
           //找到了最大值，开始滑动，并开始下一次的递归
           start = start+1;
           end = end+1;
           maxInWindowsHelper(num,start,end);
        }
    }
}