输入行数，打印杨辉三角：
如输入 5  则打印输出：
        1
       1 1
      1 2 1
     1 3 3 1
    1 4 6 3 1
但是我的却这样输出：
         1
        1 1 1
       1 2 2 2 1
      1 2 2 2 2 2 1
     1 4 4 4 4 4 4 4 1
我的代码如下，帮忙改改吧，
   #include "stdio.h"
main()
{
    int i,j,k,l,n;
    int a[1000];
    l=0;
    k=0;
    printf("please input a number:\n");
    scanf("%d",&n);
    for(i=1;i<=n;i++)
    {
        for(j=1;j<=n+i-1;j++)
        {
            if(j<=n-i)
            printf(" ");
            else
            {
                if(j==n-i+1||j==n+i-1)
                {
                    a[k]=1;
                    printf("%d ",a[k]);
                    k++;
                }
                else
                {
                    a[k]=a[k-3-l]+a[k-2-l];
                    printf("%d ",a[k]);
                    k++;
                    l++;
                }
            }
        }
        printf("\n");
    }

}

可是我的书上没有啊