{"problem":{"name":"Unique Subsequence","description":{"content":"Given is a sequence of $N$ integers $A_1,A_2,\\cdots,A_N$. Find the number of non-empty subsequences $s$ of $A$ satisfying the following condition, modulo $998244353$. *   There is only one way to ext","description_type":"Markdown"},"platform":"AtCoder","limit":{"time_limit":2000,"memory_limit":262144},"difficulty":"None","is_remote":true,"is_sync":true,"sync_url":null,"sign":"arc125_d"},"statements":[{"statement_type":"Markdown","content":"Given is a sequence of $N$ integers $A_1,A_2,\\cdots,A_N$.\nFind the number of non-empty subsequences $s$ of $A$ satisfying the following condition, modulo $998244353$.\n\n*   There is only one way to extract $s$ from $A$. Formally, there uniquely exists a sequence of indices $1 \\leq idx(1)<idx(2)<\\cdots<idx(k) \\leq N$ such that $A_{idx(i)}=s_i$ ($1 \\leq i \\leq k$), where $s=(s_1,s_2,\\cdots,s_k)$.\n\n## Constraints\n\n*   $1 \\leq N \\leq 2 \\times 10^5$\n*   $1 \\leq A_i \\leq N$\n*   All values in input are integers.\n\n## Input\n\nInput is given from Standard Input in the following format:\n\n$N$\n$A_1$ $A_2$ $\\cdots$ $A_N$\n\n[samples]","is_translate":false,"language":"English"}],"meta":{"iden":"arc125_d","tags":[],"sample_group":[["3\n1 2 1","5\n\nThe following five subsequences satisfy the condition.\n\n*   $(1,1)$\n*   $(1,2)$\n*   $(1,2,1)$\n*   $(2)$\n*   $(2,1)$\n\nThe subsequence $(1)$ does not satisfy the condition since there are two ways to extract it."],["4\n4 2 1 3","15"],["12\n1 2 3 6 9 2 3 3 9 6 1 6","1178"]],"created_at":"2026-03-03 11:01:14"}}