Given two integers n and r, find ^{n}C_{r. }Since the answer may be very large, calculate the answer modulo 10^{9}+7.
Example 1:
Input: n = 3, r = 2
Output: 3
Explaination: ^{3}C_{2} = 3.
Example 2:
Input: n = 2, r = 4
Output: 0
Explaination: r is greater than n.
Your Task:
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 ^{n}C_{r }modulo 10^{9}+7..
Expected Time Complexity: O(n*r)
Expected Auxiliary Space: O(r)
Constraints:
1 ≤ n ≤ 1000
1 ≤ r ≤ 800

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