CF Tavas and Karafs (二分)

Tavas and Karafs

time limit per test

2 seconds

memory limit per test

256 megabytes

input

standard input

output

standard output

Karafs is some kind of vegetable in shape of an 1 × h rectangle. Tavaspolis people love Karafs and they use Karafs in almost any kind of food. Tavas, himself, is crazy about Karafs.

Each Karafs has a positive integer height. Tavas has an infinite 1-based sequence of Karafses. The height of the i-th Karafs is si = A + (i - 1) × B.

For a given m, let's define an m-bite operation as decreasing the height of at most m distinct not eaten Karafses by 1. Karafs is considered as eaten when its height becomes zero.

Now SaDDas asks you n queries. In each query he gives you numbers l, t and m and you should find the largest number r such that l ≤ r and sequence sl, sl + 1, ..., sr can be eaten by performing m-bite no more than t times or print -1 if there is no such number r.

Input

The first line of input contains three integers A, B and n (1 ≤ A, B ≤ 106, 1 ≤ n ≤ 105).

Next n lines contain information about queries. i-th line contains integers l, t, m (1 ≤ l, t, m ≤ 106) for i-th query.

Output

For each query, print its answer in a single line.

Sample test(s)

input

2 1 4
1 5 3
3 3 10
7 10 2
6 4 8

output

4
-1
8
-1

input

1 5 2
1 5 10
2 7 4

output

1
2

 

 

今天才发现比赛时候的算法是对的。。。只不过数据爆了，改成long long就过了，还重新找题解写了一次。。。。

不过新写的更快一点,130ms,二分查找，下界为L,二分查上界,上界的初始值可以算出来。

 1 #include <iostream>

 2 #include <cstring>

 3 #include <algorithm>

 4 #include <cstdio>

 5 #include <ctime>

 6 using    namespace    std;

 7 

 8 long long    bsearch(long long,long long,long long);

 9 

10 long long    A,B;

11 int        main(void)

12 {

13     long long    l,t,m,r;

14     long long    n;

15     

16     scanf("%lld%lld%lld",&A,&B,&n);

17     while(n --)

18     {

19         scanf("%lld%lld%lld",&l,&t,&m);

20         if(t < A + (l - 1) * B)

21         {

22             puts("-1");

23             continue;

24         }

25         r = bsearch(l,t,m);

26         printf("%lld\n",r);

27     }

28     

29     return    0;

30 }

31 

32 long long    bsearch(long long l,long long t,long long m)

33 {

34     long long    low = l;

35     long long    high = (t - A) / B + 1;

36 

37     while(low <= high)

38     {

39         long    long    mid = (low + high) / 2;

40         long    long    box = (A + (l - 1) * B + A + (mid - 1) * B) * (mid - l + 1) / 2;

41 

42         if(box <= m * t)

43             low = mid + 1;

44         else

45             high = mid - 1;

46     }

47 

48     return    low - 1;

49 }