C. A Problem about Polyline time limit per test 1 second memory limit per test 256 megabytes
There is a polyline going through points (0, 0) – (x, x) – (2x, 0) – (3x, x) – (4x, 0) – ... - (2kx, 0) – (2kx + x, x) – ....
We know that the polyline passes through the point (a, b). Find minimum positive value x such that it is true or determine that there is no such x.
Input
Only one line containing two positive integers a and b (1 ≤ a, b ≤ 109).
Output
Output the only line containing the answer. Your answer will be considered correct if its relative or absolute error doesn't exceed 10 - 9. If there is no such x then output - 1 as the answer.
Sample test(s) Input
3 1 Output
1.000000000000 Input
1 3 Output
-1 Input
4 1 Output
1.250000000000 題解：對于a<b就是-1 隻有兩種情況： 上升段：a-2*ans*m=b;最小的ans是b是以m<=(a-b)/(2*b);可以得到ans的最小值
轉載于:https://www.cnblogs.com/zxhl/p/4816083.html