字符棱形 -- 区间跟踪

解题思路:
               无非是跟踪每一行打印输出的区间左值和右值，[first,last]
注意事项:

            总行数：5（对角线长度）

            每行字符数：1 → 3 → 5 → 3 → 1

            每行前导空格数：2 → 1 → 0 → 1 → 2

            输出的是居中对齐的菱形，不是三行连续字符

参考代码:

#include <bits/stdc++.h>

using namespace std;

int main()

 {

                  char signal ;

                  cin >> signal;

                  int n = 5;

                  int mid = n / 2;

                  int spaces;

                  int first;          //区间左值

                  int last;          //区间右值

                  for(int i = 0;i < 5;i++)

                  {

                      spaces = mid - abs(i - mid);   //计算差值

                      first =  mid - spaces;

                      last = mid + spaces;

                      for(int j = 0 ; j < n ;j++)

                      {

                                if(j < first || j > last)

                                {

                                               cout << " ";

                                }

                                else

                                {

                                               cout <<signal;

                                }

                      }

                      cout << endl;

                  }

                    return 0;

}