| Time Limit: 3000MS | Memory Limit: 65536K | |
| Total Submissions: 4284 | Accepted: 1012 |
Description
To play against the threats of malicious countries nearby, Country R has updated their missile defence system. The new type system can bring down a series of missiles as long as they are coming in ascending order by altitude or descending order by altitude.
Given the heights of a sequence of coming missiles, the general wants to know how many sets of the new type systems are needed to bring down all of them.
Input
The input consists of several test cases. The first line of each test case contains an integer n(1 ≤ n ≤ 50). The next line contains n different integers indicating the heights.
Output
For each test case output a single line containing the number of systems needed.
Sample Input
5 3 5 2 4 1 0
Sample Output
2
Hint
Two sets of systems are needed for the sample. One brings down 3, 4 and the other brings down 5, 2, 1.
Source
#include<iostream>
#include<cstdio>
#include<cstring>
#include<string>
#include<cmath>
#include<algorithm>
#include<cstdlib>
#include<queue>
#include<vector>
#include<set>
#include<stack>
#include<map>
#define INF 100000000
using namespace std;
int up[55],down[55];
int n,a[55],ans;
void dfs(int x,int y,int t)
{
if(x+y>=ans)
return ;
if(t>n)
{
if(x+y<ans)
ans=x+y;
return ;
}
int i,temp;
for(i=1;i<=x;i++)
{
if(up[i]<a[t])
break;
}
temp=up[i];
up[i]=a[t];
dfs(max(i,x),y,t+1);
up[i]=temp;
for(i=1;i<=y;i++)
{
if(down[i]>a[t])
break;
}
temp=down[i];
down[i]=a[t];
dfs(x,max(i,y),t+1);
down[i]=temp;
}
int main()
{
while(scanf("%d",&n)!=EOF)
{
if(n==0)
break;
for(int i=1;i<=n;i++)
scanf("%d",&a[i]),up[i]=0,down[i]=0;
ans=INF;
dfs(0,0,1);
printf("%d
",ans);
}
return 0;
}