题解 | 【模板】双指针

#include<bits/stdc++.h>
using namespace std;

const int N=2e5+10;

int a[N],n; 
map<int,int> num_to_count;


void solve(){
	
	int l=1,r=1,max_length=1;
	num_to_count[a[r]]++;
	vector<pair<int,int>> res_lr;
	res_lr.push_back({l,r});
	
	while(l<=r){
		r++;
		if(r>n) break;
		num_to_count[a[r]]++;
		while(num_to_count[a[r]]>1){
			num_to_count[a[l]]--;
			l++;
		}
		if(r-l+1==max_length){
			res_lr.push_back({l,r});
		}else if(r-l+1>max_length){
			max_length=r-l+1;
			res_lr.clear();
			res_lr.push_back({l,r});
		}
	}
	cout<<res_lr.size()<<endl;
	for(int i=0;i<res_lr.size();i++){
		cout<<res_lr[i].first<<" "<<res_lr[i].second<<endl;
	}
	return;
}

int main(){
	ios::sync_with_stdio(false);
	cin.tie(0);
	
	cin>>n;
	for(int i=1;i<=n;i++){
		cin>>a[i];
	}
	
	solve();

    return 0;
}