递推法：杨辉三角

def solve():
    triangle = [[1]]
    for i in range(1, 5):
        row = [1]
        for j in range(1, i):
            row.append(triangle[i-1][j-1] + triangle[i-1][j])
        row.append(1)
        triangle.append(row)
    for row in triangle:
        print(' '.join(map(str, row)))