一道关于C++二维数组的问题

输入一个值为n的数，输出这样一个n*n的序列。如何简单实现？

for example 打印一个序列：

1 2 3 4

12 13 14 5

11 16 15 6

10 9 8 7

#include <vector>
 #include <iostream>
 using namespace std;

 int main()
 {
     int n;
     int i, j;
     int t;
     int flag = 1;
     vector< vector<int> > Matrix;

     cout << "输入n: \n";
     cin >> n;
     Matrix.resize(n);
     for(i=0; i<n; i++)
         Matrix[i].resize(n);

     i = j = 0;

     for(i=0; i<n; i++)
         for(j=0; j<n; j++)
             Matrix[i][j] = -1;

     i = j = 0;
     t = 1;

     while(t <= n*n)
     {
         if(flag == 1)
         {
             if(Matrix[i][j] == -1)
             {
                 Matrix[i][j] = t;
                 j++;
                 if(j+1 >= n || Matrix[i][j+1] != -1)
                     flag = 2;
             }
         }
         else if(flag == 2)
         {
             if(Matrix[i][j] == -1)
             {
                 Matrix[i][j] = t;
                 i++;
                 if(i+1 >= n || Matrix[i+1][j] != -1)
                     flag = 3;
             }
         }
         else if(flag == 3)
         {
             if(Matrix[i][j] == -1)
             {
                 Matrix[i][j] = t;
                 j--;
                 if(j-1 < 0 || Matrix[i][j-1] != -1)
                     flag = 4;
             }
         }
         else if(flag == 4)
         {
             if(Matrix[i][j] == -1)
             {
                 Matrix[i][j] = t;
                 i--;
                 if(i-1 < 0 || Matrix[i-1][j] != -1)
                     flag = 1;
             }
         }
         ++t;
     }

     for(i=0; i<n; i++)
     {
         for(j=0; j<n; j++)
         {
             cout << Matrix[i][j];
             if(j!=n-1)
                 cout << ' ';
             else
                 cout << '\n';
         }
     }
     return 0;
 }