HDU-1011-Starship Troopers

本文介绍了一个基于树形结构的问题,即如何在有限的资源下,通过合理的路径选择来最大化捕获特定目标的概率。具体场景为指挥星舰战士在洞穴中寻找并捕获敌方大脑,通过算法实现资源利用的最大化。

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Starship Troopers

Time Limit: 10000/5000 MS (Java/Others)    Memory Limit: 65536/32768 K (Java/Others)
Total Submission(s): 20832    Accepted Submission(s): 5549


Problem Description
You, the leader of Starship Troopers, are sent to destroy a base of the bugs. The base is built underground. It is actually a huge cavern, which consists of many rooms connected with tunnels. Each room is occupied by some bugs, and their brains hide in some of the rooms. Scientists have just developed a new weapon and want to experiment it on some brains. Your task is to destroy the whole base, and capture as many brains as possible.

To kill all the bugs is always easier than to capture their brains. A map is drawn for you, with all the rooms marked by the amount of bugs inside, and the possibility of containing a brain. The cavern's structure is like a tree in such a way that there is one unique path leading to each room from the entrance. To finish the battle as soon as possible, you do not want to wait for the troopers to clear a room before advancing to the next one, instead you have to leave some troopers at each room passed to fight all the bugs inside. The troopers never re-enter a room where they have visited before.

A starship trooper can fight against 20 bugs. Since you do not have enough troopers, you can only take some of the rooms and let the nerve gas do the rest of the job. At the mean time, you should maximize the possibility of capturing a brain. To simplify the problem, just maximize the sum of all the possibilities of containing brains for the taken rooms. Making such a plan is a difficult job. You need the help of a computer.
 

Input
The input contains several test cases. The first line of each test case contains two integers N (0 < N <= 100) and M (0 <= M <= 100), which are the number of rooms in the cavern and the number of starship troopers you have, respectively. The following N lines give the description of the rooms. Each line contains two non-negative integers -- the amount of bugs inside and the possibility of containing a brain, respectively. The next N - 1 lines give the description of tunnels. Each tunnel is described by two integers, which are the indices of the two rooms it connects. Rooms are numbered from 1 and room 1 is the entrance to the cavern.

The last test case is followed by two -1's.
 

Output
For each test case, print on a single line the maximum sum of all the possibilities of containing brains for the taken rooms.
 

Sample Input
5 10 50 10 40 10 40 20 65 30 70 30 1 2 1 3 2 4 2 5 1 1 20 7 -1 -1
 

Sample Output
50 7

题意:你是舰队的舰长,然后去消灭敌人,敌人藏在一些洞里面,因为要擒贼先擒王嘛,所以我们要捕获敌人的领导者大脑,每个房间有一些虫子(电影中的虫族?=。=),消灭需要1士兵/20虫子,每个房间都给你有大脑的概率,然后让你求在士兵消耗完之前怎么走使得最后得到的概率最大。简单来说就是一棵树,给你一定的费用,每到一个点会消耗20费用,同时会获得一定的价值,然后求最大所能获得的价值。

状态转移:dp[now][i]=max(dp[now][i],dp[now][i-k]+dp[son][k]),当前点所能获得的最大价值为当前消耗k个士兵所能获得的最大价值。

代码:

#include<stdio.h>
#include<string.h>
#include<iostream>
#include<math.h>
using namespace std;
int n,m;
struct f
{
int cz,mt;
}mapp[105];
int dp[105][105];
bool bj[105];
int tree[105][105];
void dfs(int p)
{
bj[p]=true;
int s=mapp[p].cz/20;
double x=mapp[p].cz/20.0;
if(x!=s)
    s++;
for(int i=s;i<=m;i++)  dp[p][i]=mapp[p].mt;
    for(int i=1;i<=tree[p][0];i++)
        {
        int pp=tree[p][i];
        if(bj[pp])
            continue;
        dfs(pp);
        for(int j=m;j>=s;j--)
            for(int k=1;j+k<=m;k++)
                if(dp[pp][k])
                  dp[p][j+k]=max(dp[p][j+k],dp[p][j]+dp[pp][k]);
        }
}
int main()
{
int a,b;
while(cin>>n>>m)
    {
    memset(dp,0,sizeof(dp));
    memset(tree,0,sizeof(tree));
    memset(bj,false,sizeof(bj));
    if(n==-1&&m==-1)
        break;
    for(int i=1;i<=n;i++)
        scanf("%d%d",&mapp[i].cz,&mapp[i].mt);
    for(int i=1;i<n;i++)
        {
        scanf("%d%d",&a,&b);
        tree[a][0]++;
        tree[a][tree[a][0]]=b;
        tree[b][0]++;
        tree[b][tree[b][0]]=a;
        }
    if(m==0)
        cout<<0<<endl;
    else
        {
        dfs(1);
        cout<<dp[1][m]<<endl;
        }
    }
return 0;
}




HDU-3480 是一个典型的动态规划问题,其题目标题通常为 *Division*,主要涉及二维费用背包问题或优化后的动态规划策略。题目大意是:给定一个整数数组,将其划分为若干个连续的子集,每个子集最多包含 $ m $ 个元素,并且每个子集的最大值与最小值之差不能超过给定的阈值 $ t $,目标是使所有子集的划分代价总和最小。每个子集的代价是该子集最大值与最小值的差值。 ### 动态规划思路 设 $ dp[i] $ 表示前 $ i $ 个元素的最小代价。状态转移方程如下: $$ dp[i] = \min_{j=0}^{i-1} \left( dp[j] + cost(j+1, i) \right) $$ 其中 $ cost(j+1, i) $ 表示从第 $ j+1 $ 到第 $ i $ 个元素构成一个子集的代价,即 $ \max(a[j+1..i]) - \min(a[j+1..i]) $。 为了高效计算 $ cost(j+1, i) $,可以使用滑动窗口或单调队列等数据结构来维护区间最大值与最小值,从而将时间复杂度优化到可接受的范围。 ### 示例代码 以下是一个简化版本的动态规划实现,使用暴力方式计算区间代价,适用于理解问题结构: ```cpp #include <bits/stdc++.h> using namespace std; const int INF = 0x3f3f3f3f; const int MAXN = 10010; int a[MAXN]; int dp[MAXN]; int main() { int T, n, m; cin >> T; for (int Case = 1; Case <= T; ++Case) { cin >> n >> m; for (int i = 1; i <= n; ++i) cin >> a[i]; dp[0] = 0; for (int i = 1; i <= n; ++i) { dp[i] = INF; int mn = a[i], mx = a[i]; for (int j = i; j >= max(1, i - m + 1); --j) { mn = min(mn, a[j]); mx = max(mx, a[j]); if (mx - mn <= T) { dp[i] = min(dp[i], dp[j - 1] + mx - mn); } } } cout << "Case " << Case << ": " << dp[n] << endl; } return 0; } ``` ### 优化策略 - **单调队列**:可以使用两个单调队列分别维护当前窗口的最大值与最小值,从而将区间代价计算的时间复杂度从 $ O(n^2) $ 降低到 $ O(n) $。 - **斜率优化**:若问题满足特定的决策单调性,可以考虑使用斜率优化技巧进一步加速状态转移过程。 ### 时间复杂度分析 原始暴力解法的时间复杂度为 $ O(n^2) $,在 $ n \leq 10^4 $ 的情况下可能勉强通过。通过单调队列优化后,可以稳定运行于 $ O(n) $ 或 $ O(n \log n) $。 ### 应用场景 HDU-3480 的问题模型可以应用于资源调度、任务划分等场景,尤其适用于需要控制子集内部差异的问题,如图像分块压缩、数据分段处理等[^1]。 ---
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