hdu2845_简单dp

题目链接：http://acm.hdu.edu.cn/showproblem.php?pid=2845

题意：给你一个矩阵，如果取num[i][j], 那么num[i - 1][], num[i + 1][j], num[i][j - 1], num[i][j + 1]都会被删除， 问取得数的最大和是多少？

#include <iostream>
#include <cstdio>
#include <cstring>
#include <algorithm>
#include <cstdlib>
#include <cmath>
#include <set>
#include <map>
#include <vector>
#define LL long long
using namespace std;

const int N = 2 * 1e5 + 10;
LL r[N], num[N], dp[5];
int main()
{
    int n, m;
    while(~scanf("%d %d", &m, &n))
    {
        for(int i = 1; i <= m; i++)
        {     
            dp[0] = 0;
            for(int j = 1; j <= n; j++)
            {
                scanf("%lld", r + j);
                if(j == 1)
                    dp[1] = r[1];
                if(j == 2)
                    dp[2] = max(dp[1], r[2]);
                if(j > 2)
                    dp[j % 3] = max(dp[(j - 1) % 3], max(dp[(j - 2) % 3], dp[(j - 3) % 3]) + r[j]);
               // cout << dp[0] << " "<< dp[1] << " " << dp[2] << " ";
            }
            num[i] = dp[n % 3];
            //cout <<num[i] << endl;
        }        
        dp[0] = 0;
        for(int j = 1; j <= m; j++){
            if(j == 1)
                dp[1] = num[1];
            if(j == 2)
                dp[2] = max(num[1], num[2]);
            dp[j % 3] = max(dp[(j - 1) % 3], max(dp[(j - 2) % 3], dp[(j - 3) % 3]) + num[j]);
        }
        printf("%lld
", dp[m % 3]);
    }
    return 0;
}