在屏幕上显示杨辉三角形。杨辉三角形中的数，正是(x+y)的N次方幂展开式各项的系数。本题作为程序设计中具有代表性的题目，求解的方法很多，这里仅给出一种。读者可自行设计一种实现杨辉三角形的方法-In the Yang Hui triangle displayed on the screen. The number of Yang Hui triangle is (x+ y) of the N-th power of the coefficient of expansion. Program design as the title of representative of the subject, the method of solving a lot of give here only a. Readers are free to design a way to achieve the Yang Hui triangle