洛谷P4781 题解公式 inline int FastPow(int x, int y) { if (y == 1) return x; if (!y) return 1; int tmp = FastPow(x, y >> 1) % mod; return tmp * tmp % mod * (y & 1 ? x : 1) % mod; } inline void Lagrange() { go(i, 1, n, 1) { up = down = 1; go(j, 1,

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