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Problems > Distributing Identical Coins

Distributing Identical Coins

Difficulty: 1500 3000 ms 128 MB

math combinatorics

Count the ways to hand out N identical coins to K distinct children (children may receive zero), modulo 109+7.

Input: one line with two integers N and K.

Output: C(N+K−1, K−1) mod 109+7.

Constraints:

  • 0 ≤ N ≤ 105
  • 1 ≤ K ≤ 105

Sample Tests

Input 1
3 2
Output 1
4
Input 2
0 5
Output 2
1

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