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;
}