Codeforces 534B Covered Path(贪心)

时间：2015-04-13 18:59:24 阅读：181 评论：0 收藏：0 [点我收藏+]

题意你在路上走每秒钟的开始都可以改变自己的速度(改变速度都是瞬间完成的) 知道你开始的速度v1 结束时的速度v2 整个过程所用时间t 以及每秒最多改变的速度d 求这段时间内你最多走了多远

最优的肯定是先把速度从v1升到最大然后从最大减到v2 使得用的时间不会超多t 因为肯定是足够从v1减为或升到v2的那么我们只用从两端往中间靠哪边的速度小哪边就加上d 知道两边相邻这样就能保证每次改变的速度都最大而且最后两端的速度差也不会大于d 也就是最优答案了

#include <bits/stdc++.h>
using namespace std;
const int N = 105;
int v[N];
int main()
{
    int v1, v2, t, d, k;
    while(~scanf("%d%d%d%d", &v1, &v2, &t, &d))
    {
        v[0] = v1, v[t - 1] = v2;
        int le = 0, ri = t - 1, ans = 0;
        while(le < ri - 1)
        {
            if(v[le] < v[ri]) v[le + 1] = v[le++] + d;
            else v[ri - 1] = v[ri--] + d;
        }
        for(int i = 0; i < t; ++i) ans += v[i];
        printf("%d\n", ans);
    }
    return 0;
}
//Last modified :   2015-04-13 00:27

The on-board computer on Polycarp‘s car measured that the car speed at the beginning of some section of the path equals v1 meters per second, and in the end it is v2 meters per second. We know that this section of the route took exactly t seconds to pass.

Assuming that at each of the seconds the speed is constant, and between seconds the speed can change at most by d meters per second in absolute value (i.e., the difference in the speed of any two adjacent seconds does not exceed d in absolute value), find the maximum possible length of the path section in meters.

Input

The first line contains two integers v1 and v2 (1?≤?v1,?v2?≤?100) — the speeds in meters per second at the beginning of the segment and at the end of the segment, respectively.

The second line contains two integers t (2?≤?t?≤?100) — the time when the car moves along the segment in seconds, d (0?≤?d?≤?10) — the maximum value of the speed change between adjacent seconds.

It is guaranteed that there is a way to complete the segment so that:

the speed in the first second equals v1,
the speed in the last second equals v2,
the absolute value of difference of speeds between any two adjacent seconds doesn‘t exceed d.

Output

Print the maximum possible length of the path segment in meters.

Sample test(s)

input
5 6
4 2

output
26

input
10 10
10 0

output
100

Note

In the first sample the sequence of speeds of Polycarpus‘ car can look as follows: 5, 7, 8, 6. Thus, the total path is 5?+?7?+?8?+?6?=?26meters.

In the second sample, as d?=?0, the car covers the whole segment at constant speed v?=?10. In t?=?10 seconds it covers the distance of 100 meters.

Codeforces 534B Covered Path(贪心)

标签：acm 贪心

原文地址：http://blog.csdn.net/acvay/article/details/45029055

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