中文说明：分段卷积算法，用于实现两个序列直接的卷积运算。该方法比较简单，并且备有注释。便于读者理解，合适初学者学学习
English Description：
The piecewise convolution algorithm is used to realize the direct convolution of two sequences. This method is simple and has comments. Easy for readers to understand, suitable for beginners to learn