# 输入一个正整数n（代表图形的行数），输出如样例形式的图形。

输入：7

输出：

```json
    D      D
    CD    DC
    BCD  DCB
    ABCDDCBA
    BCD  DCB
    CD    DC
    D      D
```

以下程序实现了这一功能，请你填补空白处内容：

```cpp
#include <stdio.h>
#include <vector>
#include <string>
#include <iostream>
#include <algorithm>
using namespace std;
int main()
{
    int n;
    cin >> n;
    vector<string> a(n, ""), b(n, "");
    int m = (n + 1) / 2;
    int p = 0;
    for (int i = m - 1; i >= 0; i--)
    {
        for (int j = 0; j <= i; j++)
            a[i].push_back('A' + j + p);
        b[i] = a[i];
        reverse(b[i].begin(), b[i].end());
        ___________________;
        p++;
    }
    p = 0;
    for (int i = n - 1; i >= m; i--)
    {
        a[i] = a[p];
        b[i] = b[p++];
    }
    for (int i = 0; i < n; i++)
        cout << a[i] << b[i] << endl;
    return 0;
}
```


## template

```cpp
#include <stdio.h>
#include <vector>
#include <string>
#include <iostream>
#include <algorithm>
using namespace std;
int main()
{
    int n;
    cin >> n;
    vector<string> a(n, ""), b(n, "");
    int m = (n + 1) / 2;
    int p = 0;
    for (int i = m - 1; i >= 0; i--)
    {
        for (int j = 0; j <= i; j++)
            a[i].push_back('A' + j + p);
        b[i] = a[i];
        reverse(b[i].begin(), b[i].end());
        for (int j = i + 1; j < m; j++)
        {
            a[i] += " ";
            b[i] = " " + b[i];
        }
        p++;
    }
    p = 0;
    for (int i = n - 1; i >= m; i--)
    {
        a[i] = a[p];
        b[i] = b[p++];
    }
    for (int i = 0; i < n; i++)
        cout << a[i] << b[i] << endl;
    return 0;
}
```

## 答案

```cpp
for (int j = i + 1; j < m; j++)
{
    a[i] += " ";
    b[i] = " " + b[i];
}
```

## 选项

### A

```cpp
for (int j = i + 1; j < m; j++)
{
    a[i] += " ";
    b[i] += " ";
}
```

### B

```cpp
for (int j = i; j <= m; j++)
{
    a[i] += " ";
    b[i] = " " + b[i];
}
```

### C

```cpp
for (int j = i; j <= m; j++)
{
    a[i] += " ";
    b[i] += " ";
}
```