题解 | 二维斐波那契数列

MOD = 10 ** 9 + 7 # 定义取模值，用于后续防止结果过大
n, m = map(int, input().split())
dp = [[0] * (m + 1) for _ in range(n + 1)]

dp[1][1] = 1
for i in range(2, n + 1):
    dp[i][1] = dp[i - 1][1]
for j in range(2, m + 1):
    dp[1][j] = dp[1][j - 1]

for i in range(2, n + 1):
    for j in range(2, m + 1):
        dp[i][j] = (dp[i - 1][j] + dp[i][j - 1]) % MOD
print(dp[n][m])