题解 | 二维斐波那契数列

MOD = 10 ** 9 + 7
a, b = map(int, input().split())

abs = [[0] * (b + 1) for _ in range(a + 1)]  # 改正定义

abs[1][1] = 1

# 初始化第一列
if a >= 2:
    for i in range(2, a + 1):
        abs[i][1] = abs[i - 1][1]
# 初始化第一行
if b >= 2:
    for j in range(2, b + 1):
        abs[1][j] = abs[1][j - 1]

# 填充其他值
if a >= 2 and b >= 2:
    for i in range(2, a + 1):
        for j in range(2, b + 1):
            abs[i][j] = (abs[i - 1][j] + abs[i][j - 1]) % MOD

print(abs[a][b])