トヨタ自動車プログラミングコンテスト2023#2(AtCoder Beginner Contest 302)
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Problem Statement

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You are given a sequence $A=(A_1,A_2,\ldots,A_N)$ of length $N$, consisting of integers between $1$ and $4$.

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Takahashi may perform the following operation any number of times (possibly zero):

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  • choose a pair of integer $(i,j)$ such that $1\leq i<j\leq N$, and swap $A_i$ and $A_j$.
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Find the minimum number of operations required to make $A$ non-decreasing. A sequence is said to be non-decreasing if and only if $A_i\leq A_{i+1}$ for all $1\leq i\leq N-1$.

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Constraints

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  • $2 \leq N \leq 2\times 10^5$
  • $1\leq A_i \leq 4$
  • All values in the input are integers.
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Input

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The input is given from Standard Input in the following format:

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N
A_1 A_2 \ldots A_N

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Output

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Print the minimum number of operations required to make $A$ non-decreasing in a single line.

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样例

Input #1
6
3 4 1 1 2 4
Output #1
3
One can make $A$ non-decreasing with the following three operations: - Choose $(i,j)=(2,3)$ to swap $A_2$ and $A_3$, making $A=(3,1,4,1,2,4)$. - Choose $(i,j)=(1,4)$ to swap $A_1$ and $A_4$, making $A=(1,1,4,3,2,4)$. - Choose $(i,j)=(3,5)$ to swap $A_3$ and $A_5$, making $A=(1,1,2,3,4,4)$. This is the minimum number of operations because it is impossible to make $A$ non-decreasing with two or fewer operations. Thus, $3$ should be printed.
Input #2
4
2 3 4 1
Output #2
3
题目信息
题号
abc302_g
时间限制
2 s
内存限制
1024 MB

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