55 lines
895 B
Python
55 lines
895 B
Python
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def problem_p02862(input_data):
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X, Y = list(map(int, input_data.split()))
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import sys
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if (2 * Y - X) % 3 != 0 or (2 * X - Y) % 3 != 0:
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return 0
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sys.exit()
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if (2 * Y - X) < 0 or (2 * X - Y) < 0:
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return 0
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sys.exit()
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x = (2 * Y - X) // 3
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y = (2 * X - Y) // 3
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# (x+y)Cxを求める
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fac = [0 for i in range(x + y + 1)]
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inv = [0 for i in range(x + y + 1)]
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finv = [0 for i in range(x + y + 1)]
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# 初期条件
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p = 1000000007
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fac[0] = fac[1] = 1
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inv[1] = 1
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finv[0] = finv[1] = 1
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# テーブルの作成
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for i in range(2, x + y + 1):
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fac[i] = fac[i - 1] * i % p
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# p=(p//a)*a+(p%a) a^(-1)=-(p//a)*(p%a)^(-1)
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inv[i] = (-(p // i) * inv[p % i]) % p
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finv[i] = finv[i - 1] * inv[i] % p
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# 求める
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return (fac[x + y] * finv[x] % p) * finv[y] % p
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