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HDU-2602___Bone Collector —— 01背包

热度:52   发布时间:2024-01-09 11:23:10.0

原题地址:http://acm.hdu.edu.cn/showproblem.php?pid=2602

Bone Collector

Problem Description

Many years ago , in Teddy’s hometown there was a man who was called “Bone Collector”. This man like to collect varies of bones , such as dog’s , cow’s , also he went to the grave …
The bone collector had a big bag with a volume of V ,and along his trip of collecting there are a lot of bones , obviously , different bone has different value and different volume, now given the each bone’s value along his trip , can you calculate out the maximum of the total value the bone collector can get ?

 

Input

The first line contain a integer T , the number of cases.
Followed by T cases , each case three lines , the first line contain two integer N , V, (N <= 1000 , V <= 1000 )representing the number of bones and the volume of his bag. And the second line contain N integers representing the value of each bone. The third line contain N integers representing the volume of each bone.

Output

One integer per line representing the maximum of the total value (this number will be less than 231).

Sample Input

15 101 2 3 4 55 4 3 2 1

Sample Output

14

 

题目大意:

有T个示例,N块骨头,背包体积容量为V。

输入第三行为每块骨头的价值,第四行为相对应骨头的体积,问可获得最大的价值为多少。

解题思路:

01背包问题,动态规划解决问题即可

代码思路:

另取一组数组来作状态转移

核心:关键在于dp【j】=max(dp[j],dp[j-w[i]]+v[i]) 的状态转移!!

          下面再详细讲解!!!

#include<bits/stdc++.h>
using namespace std;
int w[1005];
int v[1005];
int dp[1005];int main() {int t,n,m;scanf("%d",&t);while(t--) {memset(w,0,sizeof(w));memset(v,0,sizeof(v));memset(dp,0,sizeof(dp));scanf("%d%d",&n,&m);for(int i=1; i<=n; i++)scanf("%d",&v[i]);for(int i=1; i<=n; i++)scanf("%d",&w[i]);for(int i=1; i<=n; i++) {for(int j=m; j>=0; j--) {if(j>=w[i])//注意=号dp[j]=max(dp[j],dp[j-w[i]]+v[i]); //核心状态转移方程}}printf("%d\n",dp[m]);}
}
/*
1
5 10
1 2 3 4 5
5 4 3 2 1
*/

 

核心讲解:dp【j】=max(dp[j],dp[j-w[i]]+v[i]);这一行代码联系了上一个状态(dp[j-w[i]])与现在的状态(dp[j])并通过比较,实现了状态转移。下面代码详细解释了这一步骤

for(int i=1; i<=n; i++) {for(int j=m; j>=0; j--) {if(j>=w[i])//注意=号dp[j]=max(dp[j],dp[j-w[i]]+v[i]);}for(int k=1; k<=m; k++)printf("%d ",dp[k]);printf("\n");
}

显示为:

 

可以看出每次转换时dp数组都在改变,如果没有

for(int j=m;j>=0;j--)

 

则代码可简单的理解为:背包最多能装下题目中所给的骨头,如体积为10的背包能装下体积分别为5和4的体积一块,但最后其实背包还剩余了体积为1的位置没有讨论,则通过 j-- 进行剩余补充讨论。

 

在体积不断减小的同事每次都对目前这个这个体积(目前状态)下最多能装多少已知的骨头,并通过对比之前的数据(上一次的状态)取较大值。即可获得该目标体积的最大值!!