usaco-2.2-subset-pass

开始自己用的DFS居然超时，改用DP法，呵呵，秒杀！

/*
ID: qq104801
LANG: C++
TASK: subset
*/

#include <iostream>
#include <fstream>
#include <string>
#include <vector>
#include <cstdio>

using namespace std;

int n;
size_t d[800]={0};

void test()
{    
    freopen("subset.in","r",stdin);
    freopen("subset.out","w",stdout);
    cin>>n;
    int sum=n*(n+1)/2;
    if(sum & 0x1u)
    {
        cout<<0<<endl;
        return;
    }
    sum>>=1;
    d[0]=1;
    for(int i=1;i<=n;++i)
        for(int j=sum;j>=i;--j)
            d[j]+=d[j-i];
    cout<<d[sum]/2<<endl;
}

int main () 
{        
    test();        
    return 0;
}

testdata:

USER: cn tom [qq104801]
TASK: subset
LANG: C++

Compiling...
Compile: OK

Executing...
   Test 1: TEST OK [0.005 secs, 3372 KB]
   Test 2: TEST OK [0.005 secs, 3372 KB]
   Test 3: TEST OK [0.008 secs, 3372 KB]
   Test 4: TEST OK [0.005 secs, 3372 KB]
   Test 5: TEST OK [0.005 secs, 3372 KB]
   Test 6: TEST OK [0.005 secs, 3372 KB]
   Test 7: TEST OK [0.005 secs, 3372 KB]

All tests OK.

Your program ('subset') produced all correct answers! This is your submission #3 for this problem. Congratulations!

Here are the test data inputs:

------- test 1 ----
7
------- test 2 ----
15
------- test 3 ----
24
------- test 4 ----
31
------- test 5 ----
36
------- test 6 ----
39
------- test 7 ----
37

Keep up the good work!
Thanks for your submission!