题解 | 小红的01子序列构造（easy）

#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
const int N = 3e5+10;
ll n,k;
int main()
{
    cin>>n>>k;
    string s;
    cin>>s;
    ll l=0,r;
    ll cnt = 0;
    ll cur = 0;
    ll cnt2 = 0;
    for(r=0;r<n;r++)
    {
        if(s[r]=='0')cnt++;
        else cur += cnt,cnt2++;
        while(l<r&&cur>k)
        {
            if(s[l]=='0')
            {
                cur -= cnt2;
                cnt--;
            }
            else 
            {
                cnt2--;
            }
            l++;
        }
        // cout<<l+1<<' '<<r+1<<' '<<cur<<'\n';
        if(cur==k)
        {
            cout<<l+1<<' '<<r+1<<'\n';
            return 0;
        }
    }
    cout<<-1<<'\n';
    

    return 0;
}

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