P1006传纸条_dp

维护步数，两张纸条到达的行数

#include <bits/stdc++.h>
/*
#include<ext/pb_ds/assoc_container.hpp>
#include<ext/pb_ds/hash_policy.hpp>
*/
using namespace std;

const double eps = 1e-10;
const double pi = 3.1415926535897932384626433832795;
const double eln = 2.718281828459045235360287471352;

#define f(i, a, b) for (int i = a; i <= b; i++)
#define scan(x) scanf("%d", &x)
#define mp make_pair
#define pb push_back
#define lowbit(x) (x&(-x))

#define fi first
#define se second
#define SZ(x) int((x).size())
#define all(x) x.begin(), x.end()
#define rall(x) x.rbegin(), x.rend()
#define summ(a) (accumulate(all(a), 0ll))

typedef unsigned long long ull;
typedef pair<int,int> pii;
typedef vector<int> vi;

using ll=long long;

ll a[100][100],n,m,dp[(int)200][100][100]; 
int main()
{
    ios::sync_with_stdio(false);
    cin.tie(0);
    cin>>n>>m;
    f(i,1,n)f(j,1,m)cin>>a[i][j];
    for(int i=1;i<=n+m-1;++i){
        for(int j=1;j<=n;++j){
            for(int k=1;k<=n;++k){
                if(i-j<0||i-k<0||i-j+1>m||i-k+1>m)continue;
                dp[i][j][k]=max({dp[i-1][j][k],dp[i-1][j-1][k],dp[i-1][j][k-1],dp[i-1][j-1][k-1]})+(j==k?a[j][i-j+1]:a[j][i-j+1]+a[k][i-k+1]);
            }
        }
    }
    cout<<dp[n+m-1][n][n];
    return 0;
}