P7074 [CSP-J2020] 方格取数 · znzryb

## 思路讲解

其实关键在于这个格子只能走一遍，那么可以建两个dp数组，一个从上面转移过来，一个从下面转移过来。

## AC代码

[https://www.luogu.com.cn/record/231568236](https://www.luogu.com.cn/record/231568236)



::: 源代码

```cpp
// by Gospel_rock
#include <bits/stdc++.h>
#include <vector>
#define all(vec) vec.begin(),vec.end()
#define PB push_back
#define EB emplace_back
#define EM emplace
#define FI first
#define SE second
#define pct __builtin_popcountll
#define ctz __builtin_ctzll
#define SZ(a) ((long long) a.size())
#define FOR(i, a, b) for (long long i = (a); i <= (b); ++i)
#define ROF(i, a, b) for (long long i = (a); i >= (b); --i)
#define debug(var) cerr << #var <<":"<<var<<"\n";
#define cend cerr<<"\n-----------\n"
#define lson(var) (var<<1)
#define rson(var) (var<<1|1)
#define fsp(x) fixed<<setprecision(x)
#define minn(vec) *min_element(vec.begin(),vec.end())
#define maxx(vec) *max_element(vec.begin(),vec.end())
using namespace std;
#ifdef LOCAL
template<typename T> void _print(T x) { cerr << x; }
template<typename T> void _print(vector<T> v) { cerr << "[ "; for (T i : v) _print(i), cerr << " "; cerr << "]"; }
template<typename T> void _print(set<T> s) { cerr << "{ "; for (T i : s) _print(i), cerr << " "; cerr << "}"; }
template<typename T, typename U> void _print(pair<T, U> p) { cerr << "{"; _print(p.first); cerr << ", "; _print(p.second); cerr << "}"; }
template<typename T, typename U> void _print(map<T, U> m) { cerr << "{ "; for (auto &p : m) _print(p), cerr << " "; cerr << "}"; }
template<typename T> void _print(vector<vector<T>> v){cerr<<"{\n";for (auto i : v) _print(i), cerr << "\n";cerr<<" }";}
#endif

using  ll = long long;using ull = unsigned long long;
using DB=double;using LD=long double;
using i128 = __int128;
using pdd = pair<DB,DB>;using plb = pair<ll,bool>;
using pll = pair<ll,ll>;using vll=vector<ll>;using vb=vector<bool>;
using tll = tuple<ll,ll,ll>;using vii=vector<int>;
using vpll = vector<pll>;using vtll = vector<tll>;
using vdb = vector<DB>;using vc=vector<char>;
using arr3 = array<ll,3> ;using arr2 = array<ll,2>;
using CD=complex<double>;
static constexpr ll MAXN=(ll)1e6+10,INF=(ll)1e17+3; // 1e17+3是素数 1e18+9是素数
static constexpr ll mod=(ll)1e9+7; // 998244353;
static constexpr double eps=1e-8;const double pi=acos(-1.0);
ll N,M,Q,X,K,T,lT;

inline void __();
signed main()
{
    ios::sync_with_stdio(false);
    cin.tie(0);cout.tie(0);
    
    // cin>>lT;
    // while(lT--)
        __();
    return 0;
}
/*

*/
inline void __(){
    cin>>N>>M;
    vector<vll> A(N+5,vll(M+5));
    vector<vll> dp(N+5,vll(M+5,-INF));
    vector<vll> dp2(N+5,vll(M+5,-INF));
    FOR(i,1,N){
        FOR(j,1,M){
            cin>>A[i][j];
        }
    }
    dp[0][1]=0;
    dp[1][0]=0;
    FOR(y,1,M){
        FOR(x,1,N){
            ll val=A[x][y];
            dp[x][y]=max(max(dp2[x][y-1],dp[x][y-1])+val,dp[x-1][y]+val);
        }
        ROF(x,N,1){
            ll val=A[x][y];
            dp2[x][y]=max(max(dp2[x][y-1],dp[x][y-1])+val,/* (x+1>N)?-INF: */dp2[x+1][y]+val);
        }
    }
    cout<<max(dp2[N][M],dp[N][M]);
#ifdef LOCAL
    _print(dp);
    _print(dp2);
#endif
}
/*
WA  https://www.luogu.com.cn/record/231567313
AC  https://www.luogu.com.cn/record/231568236
*/
```


:::


## 心路历程（WA，TLE，MLE……）