nCr
Medium Accuracy: 32.71% Submissions: 55515 Points: 4

Given two integers n and r, find nCr. Since the answer may be very large, calculate the answer modulo 109+7.

Example 1:

Input: n = 3, r = 2
Output: 3
Explaination: 3C2 = 3. 

Example 2:

Input: n = 2, r = 4
Output: 0
Explaination: r is greater than n.

You do not need to take input or print anything. Your task is to complete the function nCr() which takes n and r as input parameters and returns nCmodulo 109+7..

Expected Time Complexity: O(n*r)
Expected Auxiliary Space: O(r)

Constraints:
1 ≤ n ≤ 1000
1 ≤ r ≤ 800

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