[理工] [離散]-生成函數

[assassin88 (Ace)]

Determine how many integer solutions there are to x1+x2+x3+x4=18 if 0<=xi<=7
for all 1<=i<=4 and both x2 and x4 are odd.

想請問的是有沒有特別解法，因為如果生成函數解很麻煩..

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推 supergud:(1+x+x^2+...)^2(x+x^3+x^5+X^7)^2 求x^18的係數
→ assassin88:列式很簡單= =  麻煩是在後面求解
推 davidmax1:  超簡單