• 内存爆了
• 将所有新生从高到底排序，

在第i行插入新生时：

1. 人数<=该行人数
2. 如果在第一行就直接插，不在则 需要满足 ** 该行人数 <= 上一行人数**

• f[0][0][0][0][0] = 1 应该为0,为了不写+1则初始化为1;

  #include <iostream>
  #include <string.h>
  
  using namespace std;
  int n;
  long long f[31][31][31][31][31];
  int rows[6];
  int main() {
  //	freopen("a.txt","r",stdin);
  	while (cin >> n && n) {
  		memset(f,0,sizeof f);
  		memset(rows,0,sizeof rows);
  		for (int i=1; i<=n; ++i) scanf("%d",&rows[i]); 
   
  		f[0][0][0][0][0] = 1; //边界设置=0也行,每一步多写一次+1就行
  		for (int i=0; i<=rows[1]; i++) 	
  			for (int j=0; j<=rows[2]; j++) 	
  				for (int k=0; k<=rows[3]; k++)	
  					for (int a=0; a<=rows[4]; a++)	
  						for (int b=0; b<=rows[5]; b++) {
  							if ( i+1<=rows[1] )
  								f[i+1][j][k][a][b] += f[i][j][k][a][b];
  							if ( j+1<=rows[2] && j+1 <= i) // j+1<=i == j<i ，可以和上一排相等
  								f[i][j+1][k][a][b] += f[i][j][k][a][b]; 
  							if ( k+1<=rows[3] && k+1 <= i && k+1 <= j)	
  								f[i][j][k+1][a][b] += f[i][j][k][a][b];
  							if ( a+1<=rows[4] && a+1 <= i && a+1 <= j && a+1<=k)
  								f[i][j][k][a+1][b] += f[i][j][k][a][b];
  							if ( b+1<=rows[5] && b+1 <= i && b+1 <= j && b+1<=k && b+1<=a)
  								f[i][j][k][a][b+1] += f[i][j][k][a][b];
  						}  
  		cout << f[ rows[1] ][ rows[2] ][ rows[3] ][ rows[4] ][ rows[5] ] << endl;
  
  	}
  	return 0;
  }