Problem
This task consists of two parts, Part I and Part II. Note that you are not required to finish Part I in order to do Part II, and Part II is the opposite of Part I.
Alice and Bob are two frogs standing on a number line. Initially, Alice is at position $0$ and Bob is at position $N$. In one second, Alice jumps to the right by $A$ units while Bob jumps to the left by $B$ units.
During the jump, they are in mid-air. After several jumps, Bob and Alice may or may not meet at a point. Note that meeting in mid-air doesn’t count. If they’ll meet, denote that point to be position $P$.
Part I (50%)
Three integers $N, A$ and $B$ will be given. Your task is to determine the value of $P$ if they will meet with each other at some point. If they won’t meet, output $-1$.
Part II (50%)
Two integers $N$ and $P$ will be given. Your task is to find the smallest pair of $(A, B)$ where $A, B \ge 1$ such that after several jumps, Alice and Bob will meet at point $P$.
A pair $(A, B)$ is considered smallest if and only if both $A$ and $B$ are minimized. It can be shown that there is only $1$ unique solution.
It can be proven that there always exists at least one pair of $(A, B)$ such that after several jumps, Alice and Bob will meet.
Input
The first line contains an integer $T$, denoting which part the test case is.
If $T = 1$, the second line contains three integers $N, A$ and $B$.
If $T = 2$, the second line contains two integers $N$ and $P$.
Output
If $T=1$, if Alice and Bob will meet at some point $P$, output the value of $P$. Otherwise, output $-1$.
If $T=2$, output the smallest pair of $(A, B)$ such that after several jumps, Alice and Bob will meet with each other.
Subtasks
For all test cases, $2 \le N \le 10^9, 1 \le A, B \le 10^9, 0 < P < N$
| Subtask | Score | Additional Constraints |
|---|---|---|
| $1$ | $21$ |
$T = 1$ $A = B = 1$ |
| $2$ | $29$ | $T = 1$ |
| $3$ | $27$ |
$T = 2$ $N \le 100$ |
| $4$ | $23$ | $T = 2$ |
Sample Test Cases
| Input | Output | |
|---|---|---|
| 1 8 1 3 |
2 | |
Note that this test case has $T=1$, which refers to part I of this problem. After the first jump, Alice is located at $1$ while Bob is located at $5$. After the second jump, Alice is located at $2$ while Bob is located at $2$. They meet. Hence, the answer is $2$. |
||
| 2 6 4 |
2 1 | |
Note that this test case has $T=2$, which refers to part II of this problem With $A=2$ and $B=1$, after the first jump, Alice and Bob are located at $2$ and $5$ respectively. After the second jump, Alice and Bob are located at $4$ and $4$ respectively. They meet, so $(2, 1)$ is a pair of valid answer. It can also be proven that $(2, 1)$ is the smallest possible pair. |
||
Scoring: Per Subtask
Authored by s22f26
Appeared in 2026 Mini Comp 4