Problem:


Score : 100 points

Problem Statement

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

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

Find the number of ways for them to share candies, modulo 10^9 + 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.

1 \leq N \leq 100

0 \leq K \leq 10^5

0 \leq a_i \leq K

Input

Input is given from Standard Input in the following format:

N K
a_1 a_2 \ldots a_N

Output

Print the number of ways for the children to share candies, modulo 10^9 + 7.

Sample Input 1

3 4
1 2 3

Sample Output 1

5

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

1 10
9

Sample Output 2

0

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

Sample Input 3

2 0
0 0

Sample Output 3

1

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

(0, 0)

Sample Input 4

4 100000
100000 100000 100000 100000

Sample Output 4

665683269

Be sure to print the answer modulo 10^9 + 7.



Sample input:
3 4
1 2 3


Sample output:
5

Submission status: Accepted

Solution code:
#!usr/bin/env python3
from collections import defaultdict
from collections import deque
from heapq import heappush, heappop
import sys
import math
import bisect
import random
def LI(): return list(map(int, sys.stdin.readline().split()))
def I(): return int(sys.stdin.readline())
def LS():return list(map(list, sys.stdin.readline().split()))
def S(): return list(sys.stdin.readline())[:-1]
def IR(n):
    l = [None for i in range(n)]
    for i in range(n):l[i] = I()
    return l
def LIR(n):
    l = [None for i in range(n)]
    for i in range(n):l[i] = LI()
    return l
def SR(n):
    l = [None for i in range(n)]
    for i in range(n):l[i] = S()
    return l
def LSR(n):
    l = [None for i in range(n)]
    for i in range(n):l[i] = SR()
    return l
sys.setrecursionlimit(1000000)
mod = 1000000007


#A
def A():
    n,k = LI()
    a = LI()
    dp = [0 for i in range(k+1)]
    f = [0 for i in range(k+1)]
    for i in range(k+1):
        if not f[i]:
            for j in a:
                if i-j >= 0:
                    dp[i] = 1-dp[i-j]
                    if dp[i] == 0:
                        break
            else:
                dp[i] = 1
    print(["First","Second"][dp[k]])
#B
def B():
    n = I()
    a = LI()
    ma = n*(n+1)//2
    su = sum(a)
    s = [1 for i in range(n+1)]
    for i in range(1,n):
        s[i+1] = s[i]+n-i+1
    d = [None for i in range(ma+1)]
    d[0] = 0
    k = 1
    for i in range(1,n+1):
        for j in range(n+1-i):
            d[k+j] = i
        k += n+1-i
    k = n%2
    dp = [su if (d[i]+k)%2 else -su for i in range(ma+1)]
    dp[0] = 0
    if k:
        for i in range(n):
            dp[i+1] = a[n-1-i]
    else:
        for i in range(n):
            dp[i+1] = -a[n-1-i]
    for i in range(1,ma):
        r = n-1-(i-s[d[i]])
        l = r+1-d[i]
        j = i+(n-d[i])
        j2 = j+1
        if (d[i]+k)%2:
            if r < n-1:
                if a[r+1]+dp[i] > dp[j]:
                    dp[j] = a[r+1]+dp[i]
            if l > 0:
                if a[l-1]+dp[i] > dp[j2]:
                    dp[j2] = a[l-1]+dp[i]
        else:
            if r < n-1:
                if -a[r+1]+dp[i] < dp[j]:
                    dp[j] = -a[r+1]+dp[i]
            if l > 0:
                if -a[l-1]+dp[i] < dp[j2]:
                    dp[j2] = -a[l-1]+dp[i]
    print(dp[ma])
    return

#C
def C():
    def comb(a,b):
        return fact[a]*inv[b]*inv[a-b]%mod

    n,k = LI()
    a = LI()
    """
    fact = [1]
    for i in range(n+k):
        fact.append(fact[-1]*(i+1)%mod)
    inv = [1]*(n+k+1)
    inv[n+k] = pow(fact[n+k],mod-2,mod)
    for i in range(n+k)[::-1]:
        inv[i] = inv[i+1]*(i+1)%mod
    f = [comb(i+n-1,n-1) for i in range(k+1)]
    for i in a:
        for j in range(k-i)[::-1]:
            f[j+i+1] -= f[j]
            f[j+i+1] %= mod
    print(f[k])
    """
    dp = [[0]*(k+1) for i in range(n+1)]
    for i in range(k+1):
        dp[0][i] = 1
    for i in range(n):
        ni = i+1
        ai = a[i]
        for j in range(k+1):
            if j >= ai+1:
                dp[ni][j] = (dp[i][j]-dp[i][j-ai-1])%mod
            else:
                dp[ni][j] = dp[i][j]
        if i < n-1:
            for j in range(k):
                dp[ni][j+1] += dp[ni][j]
                dp[ni][j+1] %= mod
    print(dp[n][k]%mod)
    return

#D
def D():
    return

#E
def E():
    n = I()
    a = LIR(n)
    b = [1<<i for i in range(n+1)]
    dp = [0 for i in range(b[n])]
    dp[0] = 1
    for i in range(n):
        for k in range(b[n])[::-1]:
            for j in range(n):
                if a[i][j] and not b[j]&k:
                    dp[b[j]|k] += dp[k]
                    dp[b[j]|k] %= mod
    print(dp[-1])
#F
def F():
    return

#G
def G():
    return

#H
def H():
    return

#Solve
if __name__ == "__main__":
    C()

Submission status: Accepted

Solution code:
mod = 10**9+7

def comb(a,b):
      return fact[a]*inv[b]*inv[a-b]%mod
  
n,k = map(int, input().split())
a = list(map(int, input().split()))
fact = [1]
for i in range(n+k):
    fact.append(fact[-1]*(i+1)%mod)
inv = [1]*(n+k+1)
inv[n+k] = pow(fact[n+k],mod-2,mod)
for i in range(n+k)[::-1]:
    inv[i] = inv[i+1]*(i+1)%mod
f = [comb(i+n-1,n-1) for i in range(k+1)]
for i in a:
    for j in range(k-i)[::-1]:
        f[j+i+1] -= f[j]
        f[j+i+1] %= mod
print(f[k])

Submission status: Accepted

Solution code:
#!usr/bin/env python3
from collections import defaultdict
from collections import deque
from heapq import heappush, heappop
import sys
import math
import bisect
import random
def LI(): return list(map(int, sys.stdin.readline().split()))
def I(): return int(sys.stdin.readline())
def LS():return list(map(list, sys.stdin.readline().split()))
def S(): return list(sys.stdin.readline())[:-1]
def IR(n):
    l = [None for i in range(n)]
    for i in range(n):l[i] = I()
    return l
def LIR(n):
    l = [None for i in range(n)]
    for i in range(n):l[i] = LI()
    return l
def SR(n):
    l = [None for i in range(n)]
    for i in range(n):l[i] = S()
    return l
def LSR(n):
    l = [None for i in range(n)]
    for i in range(n):l[i] = SR()
    return l
sys.setrecursionlimit(1000000)
mod = 1000000007


#A
def A():
    n,k = LI()
    a = LI()
    dp = [0 for i in range(k+1)]
    f = [0 for i in range(k+1)]
    for i in range(k+1):
        if not f[i]:
            for j in a:
                if i-j >= 0:
                    dp[i] = 1-dp[i-j]
                    if dp[i] == 0:
                        break
            else:
                dp[i] = 1
    print(["First","Second"][dp[k]])
#B
def B():
    n = I()
    a = LI()
    ma = n*(n+1)//2
    su = sum(a)
    s = [1 for i in range(n+1)]
    for i in range(1,n):
        s[i+1] = s[i]+n-i+1
    d = [None for i in range(ma+1)]
    d[0] = 0
    k = 1
    for i in range(1,n+1):
        for j in range(n+1-i):
            d[k+j] = i
        k += n+1-i
    k = n%2
    dp = [su if (d[i]+k)%2 else -su for i in range(ma+1)]
    dp[0] = 0
    if k:
        for i in range(n):
            dp[i+1] = a[n-1-i]
    else:
        for i in range(n):
            dp[i+1] = -a[n-1-i]
    for i in range(1,ma):
        r = n-1-(i-s[d[i]])
        l = r+1-d[i]
        j = i+(n-d[i])
        j2 = j+1
        if (d[i]+k)%2:
            if r < n-1:
                if a[r+1]+dp[i] > dp[j]:
                    dp[j] = a[r+1]+dp[i]
            if l > 0:
                if a[l-1]+dp[i] > dp[j2]:
                    dp[j2] = a[l-1]+dp[i]
        else:
            if r < n-1:
                if -a[r+1]+dp[i] < dp[j]:
                    dp[j] = -a[r+1]+dp[i]
            if l > 0:
                if -a[l-1]+dp[i] < dp[j2]:
                    dp[j2] = -a[l-1]+dp[i]
    print(dp[ma])
    return

#C
def C():
    def comb(a,b):
        return fact[a]*inv[b]*inv[a-b]%mod

    n,k = LI()
    a = LI()
    fact = [1]
    for i in range(n+k):
        fact.append(fact[-1]*(i+1)%mod)
    inv = [1]*(n+k+1)
    inv[n+k] = pow(fact[n+k],mod-2,mod)
    for i in range(n+k)[::-1]:
        inv[i] = inv[i+1]*(i+1)%mod
    f = [comb(i+n-1,n-1) for i in range(k+1)]
    for i in a:
        for j in range(k-i)[::-1]:
            f[j+i+1] -= f[j]
            f[j+i+1] %= mod
    print(f[k])
    return

#D
def D():
    return

#E
def E():
    n = I()
    a = LIR(n)
    b = [1<<i for i in range(n+1)]
    dp = [0 for i in range(b[n])]
    dp[0] = 1
    for i in range(n):
        for k in range(b[n])[::-1]:
            for j in range(n):
                if a[i][j] and not b[j]&k:
                    dp[b[j]|k] += dp[k]
                    dp[b[j]|k] %= mod
    print(dp[-1])
#F
def F():
    return

#G
def G():
    return

#H
def H():
    return

#Solve
if __name__ == "__main__":
    C()

Submission status: Accepted

Solution code:
N, K = map(int, input().split())
a = [int(x) for x in input().split()]
mod = 10**9+7
dp = [[0] * (K+1) for i in range(N+1)]
for i in range(K+1):
    dp[0][i] = 1
for i in range(1, N+1):
    for j in range(K+1):
        tmp = 0 if j-a[i-1]-1 < 0 else dp[i-1][j-a[i-1]-1]
        dp[i][j] += dp[i-1][j]-tmp
        dp[i][j] %= mod
    if i != N:
        for j in range(K):
            dp[i][j+1] = (dp[i][j+1]+dp[i][j])%mod
print(dp[N][K])

Submission status: Accepted

Solution code:
import decimal,math
from collections import Counter,defaultdict
from fractions import gcd
from bisect import bisect_right,bisect_left
decimal.getcontext().prec = 10
n,k=map(int,raw_input().split())
arr=map(int,raw_input().split())
arr = [0]+arr
mod=10**9+7
dp = [] #(n+1)*(k+1) dp
for i in range(n+1):
	ok=[]
	for j in range(k+1):
		ok.append(0)
	dp.append(ok)	
dp[0][0]=1	
for i in range(1,n+1):
	xx=0
	for j in range(k+1):
		if(j-arr[i]-1>=0):
			xx = (xx+dp[i-1][j] - dp[i-1][j-arr[i]-1])%mod
		else:
			xx=(xx+dp[i-1][j])%mod
		dp[i][j] = (xx)%mod	
	# print i,			
print (dp[n][k])%mod

Submission status: Accepted

Solution code:
# -*- coding: utf-8 -*-

import sys
import numpy as np

def input(): return sys.stdin.readline().strip()
def ceil(a, b=1): return int(-(-a // b))
def round(x): return int((x*2+1) // 2)
def fermat(x, y, MOD): return x * pow(y, MOD-2, MOD) % MOD
def lcm(x, y): return (x * y) // gcd(x, y)
def lcm_list(nums): return reduce(lcm, nums, 1)
def gcd_list(nums): return reduce(gcd, nums, nums[0])
def INT(): return int(input())
def MAP(): return map(int, input().split())
def LIST(): return list(map(int, input().split()))
sys.setrecursionlimit(10 ** 9)
INF = float('inf')
MOD = 10 ** 9 + 7

N, K = MAP()
A = LIST()

# dp[この子までの範囲で][飴を配る総数] = 場合の数
dp = np.zeros((N+1, K+1), dtype=np.int64)
# 0番目まで(誰もいない)の範囲で0個配る場合の数は1通り
dp[0,0] = 1

for i, a in enumerate(A):
    # 今回のiを次の遷移させる区間の始点としてまとめて追加
    dp[i+1] = dp[i]
    # 今回のiをa+1個ずらして、遷移させる区間の終点としてまとめて追加
    dp[i+1,a+1:] -= dp[i,:-(a+1)]
    # 累積和すれば、元の状態からそれぞれa個先まで遷移させた状態になる
    # (区間の始点・終点の記録→累積和の流れはいもす的な感じ)
    dp[i+1] = dp[i+1].cumsum()
    dp[i+1] %= MOD

print(dp[N][K])

Submission status: Accepted

Solution code:
# -*- coding: utf-8 -*-

import sys
import numpy as np

def input(): return sys.stdin.readline().strip()
def ceil(a, b=1): return int(-(-a // b))
def round(x): return int((x*2+1) // 2)
def fermat(x, y, MOD): return x * pow(y, MOD-2, MOD) % MOD
def lcm(x, y): return (x * y) // gcd(x, y)
def lcm_list(nums): return reduce(lcm, nums, 1)
def gcd_list(nums): return reduce(gcd, nums, nums[0])
def INT(): return int(input())
def MAP(): return map(int, input().split())
def LIST(): return list(map(int, input().split()))
sys.setrecursionlimit(10 ** 9)
INF = float('inf')
MOD = 10 ** 9 + 7

N, K = MAP()
A = LIST()

# dp[この子までの範囲で][飴を配る総数] = 場合の数
dp = np.zeros((N+1, K+1), dtype=np.int64)
# 0番目まで(誰もいない)の範囲で0個配る場合の数は1通り
dp[0,0] = 1

for i, a in enumerate(A):
    # 今回のiを次の遷移させる区間の始点としてまとめて追加
    dp[i+1] = dp[i]
    # 今回のiをa+1個ずらして、遷移させる区間の終点としてまとめて追加
    dp[i+1,a+1:] -= dp[i,:-(a+1)]
    # 累積和すれば、元の状態からそれぞれa個先まで遷移させた状態になる
    # (区間の始点・終点の記録→累積和の流れはimos的な感じ)
    np.cumsum(dp[i+1], out=dp[i+1])
    dp[i+1] %= MOD

print(dp[N][K])

Submission status: Accepted

Solution code:
# -*- coding: utf-8 -*-

import sys

def input(): return sys.stdin.readline().strip()
def ceil(a, b=1): return int(-(-a // b))
def round(x): return int((x*2+1) // 2)
def fermat(x, y, MOD): return x * pow(y, MOD-2, MOD) % MOD
def lcm(x, y): return (x * y) // gcd(x, y)
def lcm_list(nums): return reduce(lcm, nums, 1)
def gcd_list(nums): return reduce(gcd, nums, nums[0])
def INT(): return int(input())
def MAP(): return map(int, input().split())
def LIST(): return list(map(int, input().split()))
sys.setrecursionlimit(10 ** 9)
INF = float('inf')
MOD = 10 ** 9 + 7

N, K = MAP()
aN = LIST()

# dp[この子までの範囲で][飴を配る総数] = 場合の数
dp = [[0] * (K+1) for i in range(N+1)]
# 0番目まで(誰もいない)の範囲で0個配る場合の数は1通り
dp[0][0] = 1

for i in range(N):
    sm = [0] * (K+2)
    # 今回送るi行について累積和を取る
    for j in range(1, K+2):
        sm[j] = sm[j-1] + dp[i][j-1]
        sm[j] %= MOD
    for j in range(K+1):
        # iが送る予定の長さに応じた区間和を取る
        dp[i+1][j] = sm[j+1] - sm[max(j-aN[i], 0)]
        dp[i+1][j] %= MOD
        # for k in range(aN[i]+1):
        #     dp[i+1][j+k] += dp[i][j]
print(dp[N][K])

Submission status: Accepted

Solution code:
# -*- coding: utf-8 -*-

import sys, re
from collections import deque, defaultdict, Counter
from math import sqrt, hypot, factorial, pi, sin, cos, radians
if sys.version_info.minor >= 5: from math import gcd
else: from fractions import gcd 
from heapq import heappop, heappush, heapify, heappushpop
from bisect import bisect_left, bisect_right
from itertools import permutations, combinations, product
from operator import itemgetter, mul
from copy import deepcopy
from functools import reduce, partial
from fractions import Fraction
from string import ascii_lowercase, ascii_uppercase, digits

def input(): return sys.stdin.readline().strip()
def ceil(a, b=1): return int(-(-a // b))
def round(x): return int((x*2+1) // 2)
def fermat(x, y, MOD): return x * pow(y, MOD-2, MOD) % MOD
def lcm(x, y): return (x * y) // gcd(x, y)
def lcm_list(nums): return reduce(lcm, nums, 1)
def gcd_list(nums): return reduce(gcd, nums, nums[0])
def INT(): return int(input())
def MAP(): return map(int, input().split())
def LIST(): return list(map(int, input().split()))
sys.setrecursionlimit(10 ** 9)
INF = float('inf')
MOD = 10 ** 9 + 7

N, K = MAP()
aN = LIST()

# dp[この子までの範囲で][飴を配る総数] = 場合の数
dp = [[0] * (K+1) for i in range(N+1)]
# 0番目まで(誰もいない)の範囲で0個配る場合の数は1通り
dp[0][0] = 1

for i in range(N):
    sm = [0] * (K+2)
    # 今回送るi行について累積和を取る
    for j in range(1, K+2):
        sm[j] = sm[j-1] + dp[i][j-1]
        sm[j] %= MOD
    for j in range(K+1):
        # iが送る予定の長さに応じた区間和を取る
        dp[i+1][j] = sm[j+1] - sm[max(j-aN[i], 0)]
        dp[i+1][j] %= MOD
        # for k in range(aN[i]+1):
        #     dp[i+1][j+k] += dp[i][j]
print(dp[N][K])

Submission status: Accepted

Solution code:
from numpy import*
n,k,*a=map(int,open(0).read().split())
b=int64([1]+[0]*k)
for i in a:b[i+1:]-=copy(b[:~i]);b=cumsum(b)%(10**9+7)
print(b[k])

Submission status: Accepted

Solution code:
from numpy import*
n,k,*a=map(int,open(0).read().split())
b=int64([1]+[0]*k)
for i in a:
  b[i+1:]-=b[:~i].copy()
  b=cumsum(b)%(10**9+7)
print(b[k])

Submission status: Accepted

Solution code:
from numpy import*
M=10**9+7
n,k,*a=map(int,open(0).read().split())
b=int64([1]+[0]*k)
for i in a:
  b[i+1:]-=b[:~i].copy()
  b=cumsum(b)%(10**9+7)
print(b[k])

Submission status: Accepted

Solution code:
def main():
  M=10**9+7
  n,k,*a=map(int,open(0).read().split())
  b=[1]+[0]*k
  for i in a:
    t,d=0,[]
    for v in b[:i+1]:
      t+=v
      t%=M
      d+=t,
    for w,v in zip(b,b[i+1:]):
      t+=v-w
      t%=M
      d+=t,
    b=d
  print(t)
main()