
USACO 2025 February Contest, Silver
Problem 3. Transforming Pairs
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Bessie the brilliant bovine has discovered a new fascination—mathematical magic! One day, while trotting through the fields of Farmer John’s ranch, she stumbles upon two enchanted piles of hay. The first pile contains $a$ bales, and the second pile contains $b$ bales ($1\le a,b\le 10^{18}$).
Next to the hay, half-buried in the dirt, she discovers an ancient scroll. As she unfurls it, glowing letters reveal a prophecy:
To fulfill the decree of the Great Grasslands, the chosen one must transform these two humble hay piles into exactly $c$ and $d$ bales—no more, no less.
Bessie realizes she can only perform the following two spells:
- She can magically conjure new bales to increase the first pile’s size by the amount currently in the second pile.
- She can magically conjure new bales to increase the second pile’s size by the amount currently in the first pile.
For each of $T$ ($1\le T\le 10^4$) independent test cases, output the minimum number of operations needed to fulfill the prophecy, or if it is impossible to do so, output -1.
INPUT FORMAT (input arrives from the terminal / stdin):
The first line contains $T$.The next $T$ lines each contain four integers $a,b,c,d$.
OUTPUT FORMAT (print output to the terminal / stdout):
Output $T$ lines, the answer to each test case.SAMPLE INPUT:
4 5 3 5 2 5 3 8 19 5 3 19 8 5 3 5 3
SAMPLE OUTPUT:
-1 3 -1 0
In the first test case, it is impossible since $b>d$ initially, but operations can only increase $b$.
In the second test case, initially the two piles have $(5, 3)$ bales. Bessie can first increase the first pile by the amount in the second pile, resulting in $(8, 3)$ bales. Bessie can then increase the second pile by the new amount in the first pile, and do this operation twice, resulting in $(8, 11)$ and finally $(8, 19)$ bales. This matches $c$ and $d$ and is the minimum number of operations to get there.
Note that the third test case has a different answer than the second because $c$ and $d$ are swapped (the order of the piles matters).
In the fourth test case, no operations are necessary.
SAMPLE INPUT:
1 1 1 1 1000000000000000000
SAMPLE OUTPUT:
999999999999999999
SCORING:
- Inputs 3-4: $\max(c, d) \le 20 \cdot\min(a, b)$
- Inputs 5-7: $T \le 10$ and $a,b,c,d\le 10^6$
- Inputs 8-12: No additional constraints
Problem credits: Benjamin Qi