Codeforces 535C Tavas and Karafs 数学归纳

 1 // File Name: c.cpp
 2 // Author: darkdream
 3 // Created Time: 2015年04月15日 星期三 01时04分48秒
 4 
 5 #include<vector>
 6 #include<list>
 7 #include<map>
 8 #include<set>
 9 #include<deque>
10 #include<stack>
11 #include<bitset>
12 #include<algorithm>
13 #include<functional>
14 #include<numeric>
15 #include<utility>
16 #include<sstream>
17 #include<iostream>
18 #include<iomanip>
19 #include<cstdio>
20 #include<cmath>
21 #include<cstdlib>
22 #include<cstring>
23 #include<ctime>
24 #define LL long long
25 
26 using namespace std;
27 LL a, b, n;
28 LL l , t, m; 
29 LL be; 
30 int ok(LL k)
31 {
32     if(((be + (k-1) * b ) + be)*k/2 <= m * t && be + (k-1) * b <= t)
33         return 1;
34     return 0 ; 
35 }
36 int solve(LL low ,LL high)
37 {
38     while(low <= high)
39     {
40         LL mid = (low + high)/2;
41         if(ok(mid))
42         {
43            low = mid + 1;
44         }else high = mid -1;
45     }
46     return high;
47 }
48 int main(){
49     scanf("%lld %lld %lld",&a,&b,&n);
50     for(LL i = 1;i <= n;i ++){
51         scanf("%lld %lld %lld",&l,&t,&m);
52         be = (l - 1) * b + a; 
53         int k = solve(1,1e6);
54         if(k < 1)
55             printf("-1\n");
56         else printf("%lld\n",k+l-1);
57     }
58 return 0;
59 }