P2878 [USACO07JAN]保护花朵Protecting the Flowers

    • 906通过
    • 2.1K提交
  • 题目提供者 FarmerJohn2
  • 评测方式 云端评测
  • 标签 排序 模拟 贪心 USACO 2007
  • 难度 普及/提高-
  • 时空限制 1000ms / 128MB

题解

  • 提示:收藏到任务计划后,可在首页查看。
  • 体验新版界面

    最新讨论 显示

    推荐的相关题目 显示

    题目描述

    Farmer John went to cut some wood and left N (2 ≤ N ≤ 100,000) cows eating the grass, as usual. When he returned, he found to his horror that the cluster of cows was in his garden eating his beautiful flowers. Wanting to minimize the subsequent damage, FJ decided to take immediate action and transport each cow back to its own barn.

    Each cow i is at a location that is Ti minutes (1 ≤ Ti ≤ 2,000,000) away from its own barn. Furthermore, while waiting for transport, she destroys Di (1 ≤ Di ≤ 100) flowers per minute. No matter how hard he tries, FJ can only transport one cow at a time back to her barn. Moving cow i to its barn requires 2 × Ti minutes (Ti to get there and Ti to return). FJ starts at the flower patch, transports the cow to its barn, and then walks back to the flowers, taking no extra time to get to the next cow that needs transport.

    Write a program to determine the order in which FJ should pick up the cows so that the total number of flowers destroyed is minimized.

    有n头奶牛跑到FJ的花园里去吃花儿了,它们分别在距离牛圈T分钟处吃花儿,每分钟会吃掉D朵卡哇伊的花儿,(此处有点拗口,不要在意细节啊!),FJ现在要将它们给弄回牛圈,但是他每次只能弄一头回去,来回用时总共为2*T分钟,在这段时间内,其它的奶牛会继续吃FJ卡哇伊的花儿,速度保持不变,当然正在被赶回牛圈的奶牛就没口福了!现在要求以一种最棒的方法来尽可能的减少花儿的损失数量,求奶牛吃掉花儿的最少朵数!

    输入输出格式

    输入格式:

    Line 1: A single integer N

    Lines 2..N+1: Each line contains two space-separated integers, Ti and Di, that describe a single cow's characteristics

    输出格式:

    Line 1: A single integer that is the minimum number of destroyed flowers

    输入输出样例

    输入样例#1: 复制
    6
    3 1
    2 5
    2 3
    3 2
    4 1
    1 6
    输出样例#1: 复制
    86

    说明

    FJ returns the cows in the following order: 6, 2, 3, 4, 1, 5. While he is transporting cow 6 to the barn, the others destroy 24 flowers; next he will take cow 2, losing 28 more of his beautiful flora. For the cows 3, 4, 1 he loses 16, 12, and 6 flowers respectively. When he picks cow 5 there are no more cows damaging the flowers, so the loss for that cow is zero. The total flowers lost this way is 24 + 28 + 16 + 12 + 6 = 86.

    提示
    标程仅供做题后或实在无思路时参考。
    请自觉、自律地使用该功能并请对自己的学习负责。
    如果发现恶意抄袭标程,将按照I类违反进行处理。