A774.Rest Stops--Silver
普及+/提高
通过率:0%
时间限制:1.00s
内存限制:128MB
题目描述
Farmer John and his personal trainer Bessie are hiking up Mount Vancowver. For
their purposes (and yours), the mountain can be represented as a long straight
trail of length L meters (1≤L≤106). Farmer John will hike the
trail at a constant travel rate of rF seconds per meter (1≤rF≤106). Since he is working on his stamina, he will not take any rest stops
along the way.
Bessie, however, is allowed to take rest stops, where she might find some
tasty grass. Of course, she cannot stop just anywhere! There are N rest
stops along the trail (1≤N≤105); the i-th stop is xi meters
from the start of the trail (0<xi<L) and has a tastiness value ci
(1≤ci≤106). If Bessie rests at stop i for t seconds, she
receives ci⋅t tastiness units.
When not at a rest stop, Bessie will be hiking at a fixed travel rate of rB
seconds per meter (1≤rB≤106). Since Bessie is young and fit,
rB is strictly less than rF.
Bessie would like to maximize her consumption of tasty grass. But she is
worried about Farmer John; she thinks that if at any point along the hike she
is behind Farmer John on the trail, he might lose all motivation to continue!
Help Bessie find the maximum total tastiness units she can obtain while making
sure that Farmer John completes the hike.
输入格式
The first line of input contains four integers: L, N, rF, and rB.
The next N lines describe the rest stops. For each i between 1 and N,
the i+1-st line contains two integers xi and ci, describing the
position of the i-th rest stop and the tastiness of the grass there.
It is guaranteed that rF>rB, and $0 < x_1 < \dots < x_N < L $. Note
that rF and rB are given in seconds per meter!
输出格式
A single integer: the maximum total tastiness units Bessie can obtain.
输入输出样例
输入#1
10 2 4 3 7 2 8 1
输出#1
15
说明/提示
In this example, it is optimal for Bessie to stop for 7 seconds at the x=7
rest stop (acquiring 14 tastiness units) and then stop for an additional 1
second at the x=8 rest stop (acquiring 1 more tastiness unit, for a total
of 15 tastiness units).