# LeetCode 4 Keys Keyboard

LeetCode 4 Keys Keyboard
Imagine you have a special keyboard with the following keys:
`Key 1: (A)`: Prints one 'A' on screen.
`Key 2: (Ctrl-A)`: Select the whole screen.
`Key 3: (Ctrl-C)`: Copy selection to buffer.
`Key 4: (Ctrl-V)`: Print buffer on screen appending it after what has already been printed.
Now, you can only press the keyboard for N times (with the above four keys), find out the maximum numbers of 'A' you can print on screen.
Example 1:

```Input: N = 3
Output: 3
Explanation:
We can at most get 3 A's on screen by pressing following key sequence:
A, A, A
```

Example 2:

```Input: N = 7
Output: 9
Explanation:
We can at most get 9 A's on screen by pressing following key sequence:
A, A, A, Ctrl A, Ctrl C, Ctrl V, Ctrl V
```

Note:

1. 1 <= N <= 50
2. Answers will be in the range of 32-bit signed integer.

• A: 打印一个字符A
• Ctrl-A: 全选
• Ctrl-C: 复制
• Ctrl-V: 粘贴

```class Solution {
public:
int maxA(int N) {
if (N <= 6)return N;
vector<int> dp(N + 1, 0);
for (int i = 1; i <= 6; ++i)dp[i] = i;
for (int i = 7; i <= N; ++i) {
for (int b = i - 3; b >= 1; --b) {
dp[i] = max(dp[i], dp[b] + dp[b] * (i - b - 2));
}
}
return dp[N];
}
};
```

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