牛客网第一场 A Monotonic Matrix

链接：https://www.nowcoder.com/acm/contest/139/A 来源：牛客网 Count the number of n x m matrices A satisfying the following condition modulo (10 9+7). * A i, j ∈ {0, 1, 2} for all 1 ≤ i ≤ n, 1 ≤ j ≤ m. * A i,

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