前缀和优化dp

#include <bits/stdc++.h>
using namespace std;
int main() {
    int n, m;
    cin >> n >> m;
    vector<vector<long long>> dp(n + 10, vector<long long>(m + 10, 0));
    vector<vector<long long>> l(n + 10, vector<long long>(m + 10, 0));
    vector<vector<long long>> r(n + 10, vector<long long>(m + 10, 0));
    vector<vector<long long>> a(n + 10, vector<long long>(m + 10,0));
    for (int i = 1; i <= n; i++) {
        for (int j = 1; j <= m; j++){
            cin>>a[i][j];
            dp[i][j] = max(l[i - 1][j - 1], r[i - 1][j + 1]) + a[i][j];
        } 
        for (int j = 1; j <= m; j++) l[i][j] = max(l[i][j - 1], dp[i][j]);
        for (int j = m; j >= 1; j--) r[i][j] = max(r[i][j + 1], dp[i][j]);
    }
    if(m==1)cout<<a[1][1];
    else cout << l[n][m] << endl;
    return 0;
}