[POI2008]Station

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题目大意: 给定一棵n个结点的树,求一个点x作为根,使得所有结点到x的距离和最小. 思路: 树形DP. 首先考虑将1作为根的情况. 很显然我们可以用一遍O(n)的DFS预处理出每个结点所对应子树大小size和子树内每个结点到这个结点的距离和sum. 这样也就相当于我们递推求出了以1作为根时各结点到它的距离和. 现在考虑将根往下转移. 假设我们现在要从u转移到v,那么显然在sum[u]的基础上,sum[v]需要变化的是(u,v)之间的连接的边. 也就是说sum[y]=sum[x]+n-size[y…

洛谷P3478 [POI2008]STA-Station

P3478 [POI2008]STA-Station 题目描述 The first stage of train system reform (that has been described in the problem Railways of the third stage of 14th Polish OI. However, one needs not be familiar with that problem in order to solve this task.) has come…

[LeetCode] Gas Station 加油站问题

There are N gas stations along a circular route, where the amount of gas at station i is gas[i]. You have a car with an unlimited gas tank and it costs cost[i] of gas to travel from station i to its next station (i+1). You begin the journey with an e…

[BZOJ1112][POI2008]砖块Klo

[BZOJ1112][POI2008]砖块Klo 试题描述 N柱砖,希望有连续K柱的高度是一样的. 你可以选择以下两个动作 1:从某柱砖的顶端拿一块砖出来,丢掉不要了. 2:从仓库中拿出一块砖,放到另一柱.仓库无限大. 现在希望用最小次数的动作完成任务. 输入第一行给出N,K. (1 ≤ k ≤ n ≤ 100000), 下面N行,每行代表这柱砖的高度.0 ≤ hi ≤ 1000000 输出最小的动作次数输入示例输出示例数据规模及约定见"输入" 题解在滑动的区间内维护中位…

[bzoj1122][POI2008]账本BBB

1122: [POI2008]账本BBB Time Limit: 10 Sec Memory Limit: 162 MBSubmit: 402 Solved: 202[Submit][Status][Discuss] Description 一个长度为n的记账单,+表示存￥1,-表示取￥1.现在发现记账单有问题.一开始本来已经存了￥p,并且知道最后账户上还有￥q.你要把记账单修改正确,使得 1:账户永远不会出现负数: 2:最后账户上还有￥q.你有2种操作: 1:对某一位取反,耗时x: 2:把…

PAT 1072. Gas Station (30)

A gas station has to be built at such a location that the minimum distance between the station and any of the residential housing is as far away as possible. However it must guarantee that all the houses are in its service range. Now given the map of…

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