Codeforces 358D. Dima and Hares (dp)

#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
#define MS(a) memset(a,0,sizeof(a))
#define MP make_pair
#define PB push_back
const int INF = 0x3f3f3f3f;
const ll INFLL = 0x3f3f3f3f3f3f3f3fLL;
inline ll read(){
    ll x=0,f=1;char ch=getchar();
    while(ch<‘0‘||ch>‘9‘){if(ch==‘-‘)f=-1;ch=getchar();}
    while(ch>=‘0‘&&ch<=‘9‘){x=x*10+ch-‘0‘;ch=getchar();}
    return x*f;
}
//////////////////////////////////////////////////////////////////////////
const int maxn = 3e3+10;

int n,a[maxn],b[maxn],c[maxn],dp[maxn][3][2];

int main(){
    cin >> n;
    for(int i=1; i<=n; i++)
        cin >> a[i];
    for(int i=1; i<=n; i++)
        cin >> b[i];
    for(int i=1; i<=n; i++)
        cin >> c[i];

    memset(dp,-INF,sizeof(dp));
    dp[1][0][0] = a[1];
    dp[1][1][1] = b[1];
    dp[1][1][0] = dp[1][2][0] = -INF;
    for(int i=2; i<=n; i++){
        dp[i][0][0] = max(dp[i-1][1][1],dp[i-1][2][0])+a[i];
        dp[i][1][0] = max(dp[i-1][1][0],dp[i-1][0][0])+b[i];
        dp[i][1][1] = max(dp[i-1][1][1],dp[i-1][2][0])+b[i];
        dp[i][2][0] = max(dp[i-1][1][0],dp[i-1][0][0])+c[i];
    }
    cout << max(dp[n][0][0],dp[n][1][0]) << endl;

    return 0;
}