题目
1739: [Usaco2005 mar]Space Elevator 太空电梯
Time Limit: 5 Sec Memory Limit: 64 MB
Description
The cows are going to space! They plan to achieve orbit by building a sort of space elevator: a giant tower of blocks. They have K (1 <= K <= 400) different types of blocks with which to build the tower. Each block of type i has height h_i (1 <= h_i <= 100) and is available in quantity c_i (1 <= c_i <= 10). Due to possible damage caused by cosmic rays, no part of a block of type i can exceed a maximum altitude a_i (1 <= a_i <= 40000). Help the cows build the tallest space elevator possible by stacking blocks on top of each other according to the rules.
牛们要到太空去了！他们打算建造一座太空电梯来送他们进入轨道．
有K(1≤K≤400)神方块，第i种有一个特定的高度hi(l≤hi≤100)，一定的存量ci(l≤ci≤10).为防宇宙射线的破坏，第i种方块的任何部分不能超过高度ai(l≤ai≤40000)． 请用这些方块堆出最高的太空电梯．
Input
* Line 1: A single integer, K * Lines 2..K+1: Each line contains three space-separated integers: h_i, a_i, and c_i. Line i+1 describes block type i.
第1行输入一个整数K.
接下来K行，每行输入三个整数hi，ai，ci．
Output
* Line 1: A single integer H, the maximum height of a tower that can be built
一个整数，表示最大高度．
Sample Input
3
7 40 3
5 23 8
2 52 6
Sample Output
48
从底部开始，先放3个方块2，之后3个方块1，接下来6个方块3．不能把3个方块1堆到4个方
块2上，因为这样最高的方块1的顶部高度超过了40.
HINT
Source
题解
Orz考完小四门的期中考试，来刷刷水题愉悦一下身心！Orz坑爹的生物一共75分钟竟然70道选择题一堆大题，我还好几周没去，呵呵~好的，这道题目其实就是做n遍有限背包~
代码
1 /*Author:WNJXYK*/
2 #include<cstdio>
3 #include<algorithm>
4 using namespace std;
5
6 struct Node{
7 int c;
8 int h;
9 int a;
10 };
11 Node k[405];
12 bool f[40005];
13 bool cmp(Node a,Node b){
14 if (a.a<b.a)return true;
15 return false;
16 }
17 int n;
18 int main(){
19 scanf("%d",&n);
20 for (int i=1;i<=n;i++) scanf("%d%d%d",&k[i].h,&k[i].a,&k[i].c);
21 f[0]=true;
22 sort(k+1,k+n+1,cmp);
23 for (int i=1;i<=n;i++){
24 for (int h=k[i].a;h>=0;h--){
25 for (int j=1;j<=k[i].c&&k[i].h*j+h<=k[i].a;j++){
26 f[k[i].h*j+h]=f[k[i].h*j+h]||f[h];
27 }
28 }
29 }
30 int Ans=0;
31 for (int i=40000;i>=0;i--)
32 if (f[i]){
33 Ans=i;
34 break;
35 }
36 printf("%d\n",Ans);
37 return 0;
38 }