### 题目描述

With highways available, driving a car from Hangzhou to any other city is easy. But since the tank capacity of a car is limited, we have to find gas stations on the way from time to time. Different gas station may give different price. You are asked to carefully design the cheapest route to go.

### 输入

For each case, the first line contains 4 positive numbers: Cmax (<= 100), the maximum capacity of the tank; D (<=30000), the distance between Hangzhou and the destination city; Davg (<=20), the average distance per unit gas that the car can run; and N (<= 500), the total number of gas stations. Then N lines follow, each contains a pair of non-negative numbers: Pi, the unit gas price, and Di (<=D), the distance between this station and Hangzhou, for i=1,…N. All the numbers in a line are separated by a space.

### 输出

For each test case, print the cheapest price in a line, accurate up to 2 decimal places. It is assumed that the tank is empty at the beginning. If it is impossible to reach the destination, print "The maximum travel distance = X" where X is the maximum possible distance the car can run, accurate up to 2 decimal places.

50 1300 12 8
6.00 1250
7.00 600
7.00 150
7.10 0
7.20 200
7.50 400
7.30 1000
6.85 300
50 1300 12 2
7.10 0
7.00 600

### 样例输出

749.17
The maximum travel distance = 1200.00

### 代码如下

``````import java.util.*;

public class Main {
static private Scanner input;
static int Cmax, D, Davg, N;
/*
* 九度oj1437 Cmax (<= 100), the maximum capacity of the tank; D (<=30000),
* the distance between Hangzhou and the destination city; Davg (<=20), the
* average distance per unit gas that the car can run; and N (<= 500), the
* total number of gas stations.
*/
private static final int INF = 1 << 30;
static int next; // 下一个要走的“贪心”位置
static Station[] s;

public static void main(String[] args) {
input = new Scanner(System.in);
s = new Station;
for (int i = 0; i < 502; i++)
s[i] = new Station(0, 0);
while (input.hasNext()) {
Cmax = input.nextInt();
D = input.nextInt();
Davg = input.nextInt();
N = input.nextInt();
for (int i = 0; i < N; i++) {
float price = input.nextFloat();
float distance = input.nextFloat();
s[i].price = price;
s[i].distance = distance;
}
Arrays.sort(s, 0, N); // 按照距离从小到大排序

/* for( int i = 0 ; i < N ; i++ )
System.out.println(s[i].price+"  "+ s[i].distance);*/

int maxDis = Cmax * Davg; // 最大可走距离
float totalCost = 0; // 花钱总数
float dis = 0; // 总共已行走的距离
float leftO = 0; // 剩余的油
int i = 0;
if (s.distance != 0 || N == 0) {
System.out.println("The maximum travel distance = 0.00");
continue;
}
while (true) {
//				System.out.println("当前的站点："+i+"当前使用金钱："+totalCost+"当前剩余油量："+leftO);
float minPrice = findMin(i, maxDis);

if (minPrice == INF) {
if (s[i].distance + maxDis >= D) {
totalCost += ((D - s[i].distance) / Davg - leftO)*1.0 * s[i].price;
System.out.printf("%.2f
", totalCost);
break;
} else {
dis = s[i].distance + maxDis;
System.out.printf("The maximum travel distance = %.2f
", dis);
break;
}
} else if (minPrice >= s[i].price) { // 当前站是可达范围内最便宜的站
if (s[i].distance + maxDis >= D) {
float needO = (float) ((D - s[i].distance)*1.0 / Davg);
if (needO <= leftO) {
System.out.printf("%.2f
", totalCost);
} else {
totalCost += (needO - leftO)* 1.0 * s[i].price;
System.out.printf("%.2f
", totalCost);
}
break;
} else {
totalCost += (Cmax - leftO) * s[i].price;
leftO = (float) (Cmax - ((s[next].distance - s[i].distance)*1.0 / Davg));
i = next;
}
} else { // 可达范围内有更便宜的站
totalCost += ((s[next].distance - s[i].distance)*1.0 / Davg - leftO) * s[i].price;
/*System.out.println("s[i].distance:"+s[i].distance);
System.out.println("s[next].distance:"+s[next].distance);
System.out.println(totalCost+"---"+s[next].distance+"\$:"+s[i].price);*/
leftO = 0;
i = next;
}
//				System.out.println(i);
}
}
}

private static float findMin(int i, double range) {
// TODO Auto-generated method stub
float maxDis = (float) (s[i].distance + range);
float minPrice = INF;
for (int j = i + 1; j < N; j++) {
if (s[j].distance <= maxDis && s[j].distance < D) { // 既在可达范围内，又在终点前
if (s[j].price <= minPrice) { // 更贵则选择最便宜的
minPrice = s[j].price;
next = j;
}
if (minPrice < s[i].price) // 若更便宜则选择最近的一个
break;
} else { // 超出范围
break;
}
}
return minPrice;
}
}

class Station implements Comparable<Station> {
float price;
float distance;

public Station(float price, float distance) {
this.distance = distance;
this.price = price;
}

@Override
public int compareTo(Station o) {
// TODO Auto-generated method stub
if (this.distance > o.distance) {
return 1;
} else if (this.distance == o.distance) {
return 0;
} else {
return -1;
}
}
}``````