CF 1743A - Password
Monocarp has forgotten the password to his mobile phone. The password consists of 4 digits from 0 to 9 (note that it can start with the digit 0).
Monocarp remembers that his password had exactly two different digits, and each of these digits appeared exactly two times in the password. Monocarp also remembers some digits which were definitely not used in the password.
You have to calculate the number of different sequences of 4 digits that could be the password for Monocarp's mobile phone (i.?e. these sequences should meet all constraints on Monocarp's password).
Input
The first line contains a single integer t (1≤t≤200) — the number of testcases.
The first line of each testcase contains a single integer n (1≤n≤8) — the number of digits for which Monocarp remembers that they were not used in the password.
The second line contains n different integers a1,a2,…an (0≤ai≤9) representing the digits that were not used in the password. Note that the digits a1,a2,…,an are given in ascending order.
Output
For each testcase, print one integer — the number of different 4-digit sequences that meet the constraints.
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Monocarp 忘記了手機(jī)密碼。 密碼由0到9的4位數(shù)字組成(注意可以以數(shù)字0開頭)。
Monocarp 記得他的密碼恰好有兩個(gè)不同的數(shù)字,并且每個(gè)數(shù)字在密碼中都出現(xiàn)了兩次。 Monocarp 還記得一些密碼中絕對(duì)沒有使用的數(shù)字。
您必須計(jì)算可能成為 Monocarp 手機(jī)密碼的不同 4 位數(shù)字序列的數(shù)量(即這些序列應(yīng)滿足 Monocarp 密碼的所有限制)。
輸入
第一行包含一個(gè)整數(shù) t (1≤t≤200) — 測(cè)試用例的數(shù)量。
每個(gè)測(cè)試用例的第一行包含一個(gè)整數(shù) n (1≤n≤8) — Monocarp 記住密碼中未使用的位數(shù)。
第二行包含n個(gè)不同的整數(shù)a1,a2,…an (0≤ai≤9),代表密碼中未使用的數(shù)字。 請(qǐng)注意,數(shù)字 a1,a2,…,an 按升序給出。
輸出
對(duì)于每個(gè)測(cè)試用例,打印一個(gè)整數(shù)——滿足約束的不同 4 位序列的數(shù)量。
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高中數(shù)學(xué)里面的排列組合,easy題目;
下面是代碼: