EXPEDI  Expedition
A group of cows grabbed a truck and ventured on an expedition deep into the jungle. Being rather poor drivers, the cows unfortunately managed to run over a rock and puncture the truck's fuel tank. The truck now leaks one unit of fuel every unit of distance it travels.
To repair the truck, the cows need to drive to the nearest town (no more than 1,000,000 units distant) down a long, winding road. On this road, between the town and the current location of the truck, there are N (1 <= N <= 10,000) fuel stops where the cows can stop to acquire additional fuel (1..100 units at each stop).
The jungle is a dangerous place for humans and is especially dangerous for cows. Therefore, the cows want to make the minimum possible number of stops for fuel on the way to the town. Fortunately, the capacity of the fuel tank on their truck is so large that there is effectively no limit to the amount of fuel it can hold. The truck is currently L units away from the town and has P units of fuel (1 <= P <= 1,000,000).
Determine the minimum number of stops needed to reach the town, or if the cows cannot reach the town at all.
Input
The first line of the input contains an integer t representing the number of test cases. Then t test cases follow. Each test case has the follwing form:
 Line 1: A single integer, N
 Lines 2..N+1: Each line contains two spaceseparated integers describing a fuel stop: The first integer is the distance from the town to the stop; the second is the amount of fuel available at that stop.
 Line N+2: Two spaceseparated integers, L and P
Output
For each test case, output a single integer giving the minimum number of fuel stops necessary to reach the town. If it is not possible to reach the town, output 1.
Example
Input: 1 4 4 4 5 2 11 5 15 10 25 10 Output: 2 Input details The truck is 25 units away from the town; the truck has 10 units of fuel. Along the road, there are 4 fuel stops at distances 4, 5, 11, and 15 from the town (so these are initially at distances 21, 20, 14, and 10 from the truck). These fuel stops can supply up to 4, 2, 5, and 10 units of fuel, respectively. Output details: Drive 10 units, stop to acquire 10 more units of fuel, drive 4 more units, stop to acquire 5 more units of fuel, then drive to the town.
hide comments
cyg_andreih:
20190111 11:56:19
1 ? 

ankur314:
20181209 10:18:09
Wonderful Problem!!


aman_sachin200:
20180607 00:04:41
Awesome Problem!!! 

ameyanator:
20180315 17:01:01
Really Nice Question. I wouldn't have even thought of using a priority queue if the question wasn't tagged as heaps on codechef's page. Its easy to think of the solution once you know that heaps are being used. :) 

harshit_99:
20171223 17:54:08
Last edit: 20171223 17:54:25 

gboduljak:
20170602 22:55:44
can this be solved with binary search? tried but failed 

Shubham Jadhav:
20170527 11:57:00
Really nice problem :) 

iloveher:
20170519 14:49:57
Nice Problem !!!!


Dwarika Pandey:
20170204 18:23:55
Priority Queue :) 

baadshah_:
20160629 16:01:39
Finally AC!!

Added by:  Duc 
Date:  20050503 
Time limit:  2.307s 
Source limit:  50000B 
Memory limit:  1536MB 
Cluster:  Cube (Intel G860) 
Languages:  All except: NODEJS PERL6 VB.NET 
Resource:  US Open International 2005 Gold Division 