滑動窗口，單調棧模板

單調隊列，滑動窗口

題目鏈接：https://www.acwing.com/problem/content/156/

滑動窗口，維護一個大小爲k的隊列，使其隊列裏面的值是單調的。

import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.OutputStreamWriter;

public class Main {
    static BufferedReader bf = new BufferedReader(new InputStreamReader(System.in));
    static BufferedWriter bw = new BufferedWriter(new OutputStreamWriter(System.out));
    static final int N = (int)1e6 + 10;
    // 隊列中存下標
    static int[] q = new int[N];
    static int hh = 0, tt = -1;
    public static void main(String[] args) throws IOException {
        String[] str = bf.readLine().split(" ");
        int n = Integer.parseInt(str[0]);
        int k = Integer.parseInt(str[1]);
        int[] a = new int[n + 1];
        String[] str1 = bf.readLine().split(" ");
        for(int i = 0 ; i < n; i++) {
            a[i] = Integer.parseInt(str1[i]); // 輸入
            // 當下標 離 i的距離大於 k時，出隊
            if(i - k + 1 > q[hh])hh++;
            // 當a[i] 小於 a[q[tt]] 時， 出隊（維護最小的在隊首）
            while(hh <= tt && a[i] <= a[q[tt]])tt--;
            // 入隊
            q[++tt] = i;
            if(i + 1 >= k)bw.write(a[q[hh]] + " ");
        }
        bw.write("\n");
        hh = 0; tt = -1;
        for(int i = 0 ; i < n; i++) {
            a[i] = Integer.parseInt(str1[i]);
            if(i - k + 1 > q[hh])hh++;
            // 反之 依然
            while(hh <= tt && a[i] >= a[q[tt]])tt--;

            q[++tt] = i;
            if(i + 1 >= k)bw.write(a[q[hh]] + " ");
        }
        bw.write("\n");
        bw.flush();
    }

}

單調棧

棧內元素單調；

題目鏈接：https://www.acwing.com/problem/content/832/

import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.OutputStreamWriter;
import java.util.Stack;


public class Main {
    static BufferedReader bf = new BufferedReader(new InputStreamReader(System.in));
    static BufferedWriter bw = new BufferedWriter(new OutputStreamWriter(System.out));
    public static void main(String[] args) throws Exception {
        int n = Integer.valueOf(bf.readLine());
        String[] str = bf.readLine().split(" ");
        int[] a = new int[n];

        Stack<Integer> stack = new Stack<Integer>();
        for(int i = 0; i < n; i++) a[i] = Integer.valueOf(str[i]);

        for(int i = 0; i < n; i++) {
            //			int ans = -1; 如果棧內 從底 到 Top是 從大到小的，保證每次peek都是最大的
            while(!stack.isEmpty() && stack.peek() >= a[i]) {
                stack.pop();
            }
            if(stack.isEmpty())bw.write("-1 ");
            else bw.write(Integer.valueOf(stack.peek()).toString() + " ");
            stack.push(a[i]);
        }
        bw.flush();

    }

}