The 3 most upvoted explained solutions (with the most popularity) are all wrong.
The first solution doesn’t handle the case where a > b && b < c.
Failing case:
1
3 1 4
Expected: 3, Actual: -1
The second solution tries to use binary search. But there is no property that makes binary search applicable.
Failing case:
1
536870912 536870913 536870915
Expected: 0, Actual: -1
The third solution thinks a valid X can only be in the range of 0…9. This is not the case.
Failing case:
1
40000 30000 20000
Expected: 1073721823, Actual: -1
Please add some more tests to this problem. And also do something against these wrong solutions.
It would maybe help to make dislikes public viewable so you can more easily tell if the solution is wrong or not.