Watering Grass
Input: standard input
Output: standard output
Time Limit: 3 seconds
n sprinklers areinstalled in a horizontal strip of grass l meters long andwmeters wide. Each sprinkler is installed at the horizontal center line of thestrip. For each sprinkler we are given its position as the distance from theleft end of the center line and its radius of operation.
What is the minimum number of sprinklers to turnon in order to water the entire strip of grass?
Input
Input consists of a number ofcases. The first line for each case contains integer numbersn, land w with n <= 10000. The next n lines containtwo integers giving the position of a sprinkler and its radius of operation.(The picture above illustrates the first case from the sample input.)
Output
For each test case output the minimum number of sprinklers needed to waterthe entire strip of grass. If it is impossible to water the entire strip output-1.
Sample input
8 20 2
5 3
4 1
1 2
7 2
10 2
13 3
16 2
19 4
3 10 1
3 5
9 3
6 1
3 10 1
5 3
1 1
9 1
Sample Output
6
2
-1
(Regionals 2002 Warm-up Contest, Problem setter: Piotr Rudnicku)
贪心，主要就是精度问题。
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