题面#

We will call a string consisting of characters 0, 2, 5, and/or 6 a New Year string if at least one of the two conditions is met:

• it contains the string 2026 as a continuous substring;
• it does not contain the string 2025 as a continuous substring.

For example, the strings 20252026, 21026, 20262026, 000 are New Year strings. The strings 2025, 20256, 20252025, 000202500020226 are not New Year strings.

You are given a string $s$. You can perform the following operation any number of times (possibly zero):

• choose a character in the string $s$ and replace it with 0, 2, 5, or 6 (you can choose any one of these four characters).

Calculate the minimum number of operations needed to make the string $s$ a New Year string.

Input

The first line contains one integer $t$ ($1 \le t \le 10^4$) — the number of test cases.

Each test case consists of two lines:

• the first line contains one integer $n$ ($4 \le n \le 20$) — the number of characters in $s$;
• the second line contains $s$ — a sequence of $n$ characters 0, 2, 5, and/or 6.

Output

For each test case, output one integer — the minimum number of operations needed to make the string $s$ a New Year string.

思路#

理清题意，满足题目要求的字符串只需要下面两个条件至少满足一个即可：

• 包含子串 2026
• 不包含子串 2025

所以如果一个字符串不满足要求，那么它一定不包含子串 2026 且包含 2025

注意到我们只需要一次修改，将 2025 改为 2026 即可让字符串满足要求

所以答案只能是 $0$ 或者 $1$

代码#

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#include <bits/stdc++.h>
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using namespace std;
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int main() {
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    int t;
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    cin >> t;
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    while (t --) {
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        int n;
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        cin >> n;
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        string s;
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        cin >> s;
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        bool a = (s.find("2025") != string::npos);
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        bool b = (s.find("2026") != string::npos);
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        if (b || !a) cout << 0 << endl;
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        else cout << 1 << endl;
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    }
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}