CF1000D Yet Another Problem On a Subsequence

**题目大意：** 如果一个数组$[a_1,a_2,a_3,...,a_n]a_1=n-1$并且$a1>0$，这个数组就被叫为好数组，如果一个序列能正好分为多个好数组，ta就被叫为好序列，现在给定一个序列，求这个序列有多少好子序列，答案对$998244353$取模

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In the first test case, two good subsequences — $ [a_1, a_2, a_3] $ and $ [a_2, a_3] $ . In the second test case, seven good subsequences — $ [a_1, a_2, a_3, a_4], [a_1, a_2], [a_1, a_3], [a_1, a_4], [a_2, a_3], [a_2, a_4] $ and $ [a_3, a_4] $ .