# [UVA10382]Watering

Posted by John on 2016-01-21
Words 755 and Reading Time 3 Minutes
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n sprinklers are installed in a horizontal strip of grass l meters long and w meters wide. Each sprinkler is installed at the horizontal center line of the strip. For each sprinkler we are given its position as the distance from the left end of the center line and its radius of operation. What is the minimum number of sprinklers to turn on in order to water the entire strip of grass?

## Input

Input consists of a number of cases. The ﬁrst line for each case contains integer numbers n, l and w with n ≤ 10000. The next n lines contain two 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 water the 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

CPE上的測資真的弱到爆，CPE過了拿去UVA居然沒過，為此DEBUG好久……後來結論是我在for判斷的時候是以圓圈的數量作為條件，所以如果是最後一個點才完成覆蓋所有面積，這樣的情形我就不會判斷到，所以要移動一下判斷的位置

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