题解 | 小红的01子序列构造（easy）

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

int main() {
    LL n, k;
    cin >> n >> k;
    string s;
    cin >> s;
    int cnt0 = 0, cnt1 = 0;
    int l = 0, r = 0;
    if (s[0] == '0') cnt0 ++;
    if (s[0] == '1') cnt1 ++;
    LL num = 0;
    while (l < n && r < n) {
        if (num == k) {
            cout << l + 1 << ' ' << r + 1 << endl;
            return 0;
        }
        if (num < k) {
            r ++;
            if (s[r] == '0') cnt0 ++;
            else {
                num += cnt0;
                cnt1 ++;
            }
        } else {
            if (s[l] == '0') {
                num -= cnt1;
                cnt0 --;
            } else cnt1 --;
            l ++;
        }
    }
    cout << -1 << endl;
    return 0;
}