题解 | 【模板】双指针

import java.util.*;
import java.io.*;

public class Main {
    public static void main(String[] args) {
        Scanner in = new Scanner(new BufferedInputStream(System.in));
        PrintWriter out = new PrintWriter(System.out);
        int n = in.nextInt();
        int[] nums = new int[n + 1];
        ArrayList<Integer> ans = new ArrayList<>();
        int res = 0;
        
        // 核心：HashSet，用于O(1)判断元素是否存在
        Queue<Integer> queue = new ArrayDeque<>();
        Set<Integer> set = new HashSet<>();
        
        for (int i = 1; i <= n; i++) {
            nums[i] = in.nextInt();
            
            // 用set.contains替代queue.contains（O(1) vs O(k)）
            while (set.contains(nums[i])) {
                // 移除队列元素时，同步从set中移除
                int removeNum = queue.poll();
                set.remove(removeNum);
            }
            
            // 入队时同步加入set
            queue.offer(nums[i]);
            set.add(nums[i]);
            
            if (queue.size() > res) {
                res = queue.size();
                ans.clear();
                ans.add(i);
            } else if (queue.size() == res) {
                ans.add(i);
            }
        }
        
        out.println(ans.size());
        for (int end : ans) {
            out.println((end - res + 1) + " " + end);
        }
        out.flush();
    }
}