学步园

code

#include <set>
#include <map>
#include <ctime>
#include <queue>
#include <cmath>
#include <stack>
#include <limits>
#include <vector>
#include <bitset>
#include <string>
#include <cstdio>
#include <cstring>
#include <fstream>
#include <string.h>
#include <iostream>
#include <algorithm>
#define LL long long
#define Vi vector<int>
#define Si set<int>
#define readf freopen("input.txt","r",stdin)
#define writef freopen("output.txt","w",stdout)
#define FF(i,a) for(int i(0); i < (a); i++)
#define FD(i,a) for(int i(a); i >= (1); i--)
#define FOR(i,a,b) for(int i(a);i <= (b); i++)
#define FOD(i,a,b) for(int i(a);i >= (b); i--)
#define PD(a) printf("%d\n",a)
#define SET(a,b) memset(a,b,sizeof(a))
#define SD(a) scanf("%d",&(a))
#define LN printf("\n")
#define PS printf(" ")
#define pb push_back
#define lson l , m , rt << 1
#define rson m + 1 , r , rt << 1 | 1
const double pi = acos(-1.0);
const int maxn = 51;
const int INF = 99999999;
const int dx[]={0,1,0,-1};
const int dy[]={1,0,-1,0};
using namespace std;
int f[maxn][maxn][maxn][maxn],a[maxn][maxn];
int dp(int x1,int y1,int x2,int y2){
    if(f[x1][y1][x2][y2]!=0) return f[x1][y1][x2][y2];
    if(x1<1||x2<1||y1<1||y2<1)  return f[x1][y1][x2][y2];
    int ans=0;
    ans=max(ans,dp(x1-1,y1,x2-1,y2));
    ans=max(ans,dp(x1-1,y1,x2,y2-1));
    ans=max(ans,dp(x1,y1-1,x2,y2-1));
    ans=max(ans,dp(x1,y1-1,x2-1,y2));
    if(x1==x2 && y1== y2)   //此处不太明白，是看了别人的解题报告中这么写的，
        f[x1][y1][x2][y2]=ans+a[x1][y1];//但是明显一个点不能走两次 ，晕
    else
        f[x1][y1][x2][y2]=ans+a[x1][y1]+a[x2][y2];
    return  f[x1][y1][x2][y2];
}
int main(){
//    readf;
//    writef;
    int M,N;
    SD(M);SD(N);
    FOR(i,1,M) FOR(j,1,N) SD(a[i][j]);
    dp(M,N,M,N);
    //FOR(i,1,M) FOR(j,1,N) FOR(k,1,M) FOR(l,1,N){
       // printf("f[%d][%d][%d][%d]==%d\n",i,j,k,l,f[i][j][k][l]);
    //}
    printf("%d\n",f[M][N][M][N]);
    return 0;
}