Wrong Answer.wrong answer On line 1 column 1, read (ASCII 0), expected m.

#include <bits/stdc++.h>
using namespace std;
string a[3];
int cnt[3];
int main() {
	int T, id, n, k;
	cin >> T >> id;
	while(T--) {
		cin >> n >> k >> a[0];
		k = min(k, 2);
		cnt[0] = n;
		if (n <= 2) {
			cout << a[0] << "\n";
			continue;
		}
		cnt[1] = cnt[2] = 2; // 至少长度为2
		for (int j = 1; j <= k; j++) { // 删 k 次。 
			a[j] = "";
			a[j] += a[j-1][0];
			for (int i = 1; i < cnt[j-1] - 1; i++) { // 显然a[][0]和a[][n-1]不可能被删掉 
				if (a[j-1][i-1] == a[j-1][i+1]) continue;
				a[j] += a[j-1][i];
				cnt[j]++;
			}
			a[j] += a[j-1][cnt[j-1] - 1];
		}
		cout << a[k] << "\n";
	}
}