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  1. Prepare
  2. Algorithms
  3. Dynamic Programming
  4. Construct the Array
  5. Discussions

Construct the Array

  • ducminh2004pd
     + 0 comments
    long countArray(int n, int k, int x) {
    // index 0 <= i <= n-1
    vector<long> a(n); // number of array with length 1 <= i+1 <= n end with x
    vector<long> b(n); // number of array with length 1 <= i+1 <= n not end with x
    if (x == 1) {
        a[0] = 1;
        b[0] = 0;
    } else {
        a[0] = 0;
        b[0] = 1;
    }
    
    for (int i=1; i<n; i++) {
        b[i] = a[i-1] * (k-1) + b[i-1] * (k-2);
        b[i] %= 1000000007;
        a[i] = b[i-1];
    }
    
    return a[n-1] % 1000000007;
}