Choose but not both
Practice
2.8 (13 votes)
Algorithms
Depth first search
Dynamic programming
Graphs
Trees
Problem
89% Success 1550 Attempts 50 Points 2s Time Limit 256MB Memory 1024 KB Max Code
The alone Y has another array \(a_1, a_2, ..., a_n\) that \(1 \leq a_i \leq n\). this time Y wants to choose some numbers from \(1\) to \(n\) that there is no \(i\) that both \(i\) and \(a_i\) is chosen.
What is the maximum amount of numbers that Y can choose?
Input
First line contains only \(n\), legnth of array.
Second line contains the array elements \(a_1, a_2, ..., a_n\)separated by space.
\(1 \leq n \leq 3 \times 10^5\)
\(1 \leq a_i \leq n\)
Output
The only line of output contains an integer, maximum amount of numbers that Y can choose.
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