看过网上的一些方法，觉得思路很麻烦，所以自己写了一个。这个是满分答案，思路很简单。

#include <stdio.h>
#include <stdlib.h>

int main()
{
    int n;
    scanf( "%d", &n );
    int **a;
    a = (int**)malloc(sizeof(int*) * n);
    for( int i = 0; i < n; i++ )
        a[i] = (int*)malloc(sizeof(int) * n);
    
    for( int i = 0; i < n; i++ )
        for( int j = 0; j < n; j++ )
            scanf( "%d", &a[i][j] );
    
    for( int i = 0; i < n; i++ )
        for( int j = i; j >= 0; j-- )
        {
            if( i % 2 == 0 )
                printf( "%d ", a[j][i - j] );	
            else
                printf( "%d ", a[i - j][j] );
        }

    int m = n;
    for( int i = 1; i < n; i++ )	
    {
        for( int j = i; j < n; j++ )
        {
            if( n % 2 == 1 )
            {
                if( i % 2 == 1 )
                    printf( "%d ", a[j][m - j] );	
                else
                    printf( "%d ", a[m - j][j] );
            }
            
            else
            {
                if( i % 2 == 1 )
                    printf( "%d ", a[m - j][j] );	
                else
                    printf( "%d ", a[j][m - j] );
            }
            
        }
        
        m++;
    }	
        
    return 0;
}