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O(n)

long countArray(int n, long k, int x) { int mod = 1000000007; long X = k-1, Y = k-2, sum = ((k-1) * (k-1)) % mod; for (int i=2; i <= n-3; i++) { X = (sum - X) % mod; Y = (sum - Y) % mod; sum = (X + Y*(k-1)) % mod; } if (x == 1) return (sum - X + mod) % mod; else return (sum - Y + mod) % mod; }

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## Construct the Array

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O(n)