Editorial for An Animal Contest 5 P1 - Bamboo Cookies

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Author: sjay05

Subtask 1 + 2

Any two pairs $(i, j)$ ~(i, j)~ can be paired to sum to an even number as all $a_i$ ~a_i~ equal $1$ ~1~ or $2$ ~2~. The operation can be performed $\lfloor \frac{n}{2} \rfloor$ ~\lfloor \frac{n}{2} \rfloor~ times.

Time Complexity: $\mathcal{O}(1)$ ~\mathcal{O}(1)~

Subtask 3

If $N = 1$ ~N = 1~, the answer is $0$ ~0~.
If $N = 2$ ~N = 2~, the answer can be $0$ ~0~ or $1$ ~1~.
If $N = 3$ ~N = 3~, the answer is $1$ ~1~.

Time Complexity: $\mathcal{O}(1)$ ~\mathcal{O}(1)~

Subtask 4

An even number can only be created by summing two even or two odd numbers. The answer is $\lfloor \frac{\text{odd}}{2} \rfloor + \lfloor \frac{\text{even}}{2} \rfloor$ where $\text{odd}$ ~\text{odd}~ and $\text{even}$ ~\text{even}~ are the number of odd and even values in $a$ ~a~.

Time Complexity: $\mathcal{O}(N)$ ~\mathcal{O}(N)~

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