HDU 2124Repair the Wall（贪心）

Description

Long time ago , Kitty lived in a small village. The air was fresh and the scenery was very beautiful. The only thing that troubled her is the typhoon.

When the typhoon came, everything is terrible. It kept blowing and raining for a long time. And what made the situation worse was that all of Kitty's walls were made of wood.

One day, Kitty found that there was a crack in the wall. The shape of the crack is

a rectangle with the size of 1×L (in inch). Luckly Kitty got N blocks and a saw(锯子) from her neighbors.

The shape of the blocks were rectangle too, and the width of all blocks were 1 inch. So, with the help of saw, Kitty could cut down some of the blocks(of course she could use it directly without cutting) and put them in the crack, and the wall may be repaired
perfectly, without any gap.

Now, Kitty knew the size of each blocks, and wanted to use as fewer as possible of the blocks to repair the wall, could you help her ?

Input

The problem contains many test cases, please process to the end of file( EOF ).

Each test case contains two lines.

In the first line, there are two integers L(0<L<1000000000) and N(0<=N<600) which

mentioned above.

In the second line, there are N positive integers. The i th integer Ai(0<Ai<1000000000 ) means that the i th block has the size of 1×Ai (in inch).

Output

For each test case , print an integer which represents the minimal number of blocks are needed.

If Kitty could not repair the wall, just print "impossible" instead.

Sample Input

5 3

3 2 1

5 2

2 1

Sample Output

2
impossible

题意：一个人家墙破了个洞，告诉你这个洞是1×n的，你有几块木板和锯子（可以将木板裁小），问最少需要几块木板。
思路：贪心算法，局部最优解，从最大的木板往后排，如果大木板无法补全，再用小木板补，最后计算用了多少块就行了。
代码：

#include<stdio.h>
#include<iostream>
#include<algorithm>
using namespace std;
bool cmp(int x,int y)
{
return x>y;
}
int main()
{
int l,n;
while(scanf("%d %d",&l,&n)!=EOF)
{
int a[1001];
for(int i=0;i<n;i++)
scanf("%d",&a[i]);
sort(a,a+n,cmp);
int k=0;
int p=0;
for(int i=0;i<n;i++)
{
if(a[i]>=l)
{
k++;
p++;
printf("%d\n",k);
break;
}
else
{
l-=a[i];
k++;
}
}
if(p==0)
printf("impossible\n");
}
return 0;
}