HDOJ 4597 Play Game

题意:A和B玩一个游戏,有两组卡片,每张卡片有一个点数,两人轮流从任意一组的最左端或者最右端取一张,两人都足够聪明。选取一种最优的方案,使得A获得的点数和最高。

链接:http://acm.hdu.edu.cn/showproblem.php?pid=4597

思路:区间DP(记忆化搜索),取的方式从两种变成四种,状态转移方程为 ans = max ( ans, sum-dfs(a-1, b,c, d), sum-dfs(a,b-1,c,d),sum-dfs(a,b,c-1,d),sum-dfs(a,b,c,d-1))

注意点:注意边界问题,开始没考虑到边界,参考了bin神的代码,发现边界问题,然后A了。

以下为AC代码:

Run ID Submit Time Judge Status Pro.ID Exe.Time Exe.Memory Code Len. Language Author
12433404 2014-12-08 21:07:22 Accepted 4597 109MS 4348K 2073 B G++ luminous11
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#define ll long long
#define ull unsigned long long
#define all(x) (x).begin(), (x).end()
#define clr(a, v) memset( a , v , sizeof(a) )
#define pb push_back
#define mp make_pair
#define read(f) freopen(f, "r", stdin)
#define write(f) freopen(f, "w", stdout)
using namespace std;
int num1[30];
int num2[30];
int sum1[30];
int sum2[30];
int dp[30][30][30][30];
int sum = 0;
struct node
{
    int a;
    int b;
}cnt[2];
int dfs( int a, int b, int c, int d )
{
    int sum = 0;
    int ans = 0;
    if ( dp[a][b][c][d] != -1 )
        return dp[a][b][c][d];
    if ( a > b && c > d )
        return dp[a][b][c][d] = 0;
    if ( a <= b )
    {
        sum += sum1[b] - sum1[a-1];
    }
    if ( c <= d )
    {
        sum += sum2[d] - sum2[c-1];
    }
    if ( a <= b )
    {
        ans = max ( ans, sum - dfs (a + 1, b, c, d ) );
        ans = max ( ans, sum - dfs ( a, b - 1, c, d ) );
    }
    if ( c <= d )
    {
        ans = max ( ans, sum - dfs ( a, b, c + 1, d ) );
        ans = max ( ans, sum - dfs ( a, b, c, d - 1 ) );
    }
    return dp[a][b][c][d] = ans;
}
int main()
{
    ios::sync_with_stdio( false );
    int t;
    cin >> t;
    while ( t -- )
    {
        int k;
        cin >> k;
        memset ( dp, -1, sizeof ( dp ) );
        memset ( sum1, 0, sizeof ( sum1 ) );
        memset ( sum2, 0, sizeof ( sum2 ) );
        for ( int i = 1; i <= k; i ++ )
        {
            cin >> num1[i];
            sum1[i] = sum1[i-1] + num1[i];
        }
        for ( int i = 1; i <= k; i ++ )
        {
            cin >> num2[i];
            sum2[i] = sum2[i-1] + num2[i];
        }
        cout << dfs( 1, k, 1, k ) << endl;

    }
    return 0;
}


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