Educational DP Contest AtCoder M - Candies

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Points: 12
Time limit: 1.0s
Memory limit: 1G

Problem type

There are N children, numbered 1,2,,N.

They have decided to share K candies among themselves. Here, for each i (1iN), Child i must receive between 0 and ai candies (inclusive). Also, no candies should be left over.

Find the number of ways for them to share candies, modulo 109+7. Here, two ways are said to be different when there exists a child who receives a different number of candies.

Constraints

  • All values in input are integers.
  • 1N100
  • 0K105
  • 0aiK

Input Specification

The first line will contain 2 space separated integers N and K.

The next line will contain N integers, a1,a2,,aN.

Output Specification

Print the number of ways for the children to share candies, modulo 109+7.

Note: Be sure to print the answer modulo 109+7.

Sample Input 1

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3 4
1 2 3

Sample Output 1

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5

Explanation for Sample 1

There are five ways for the children to share candies, as follows:

  • (0,1,3)
  • (0,2,2)
  • (1,0,3)
  • (1,1,2)
  • (1,2,1)

Here, in each sequence, the i-th element represents the number of candies that Child i receives.

Sample Input 2

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1 10
9

Sample Output 2

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0

Explanation for Sample 2

There may be no ways for the children to share candies.

Sample Input 3

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2 0
0 0

Sample Output 3

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1

Explanation for Sample 3

There is one way for the children to share candies, as follows:

  • (0,0)

Sample Input 4

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4 100000
100000 100000 100000 100000

Sample Output 4

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665683269

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