递推DP Codeforces Round #260 (Div. 1) A. Boredom

题目传送门

 /*
     DP：从1到最大值，dp[i][1/0] 选或不选，递推更新最大值
 */
 #include <cstdio>
 #include <algorithm>
 #include <cmath>
 #include <cstring>
 using namespace std;
 typedef long long ll;
 const int MAXN = 1e5 + ;
 const int INF = 0x3f3f3f3f;
 ll dp[MAXN][];
 ll cnt[MAXN];
 ll work(int mx)
 {
     ll ret = ;
     for (int i=; i<=mx; ++i)
     {
         dp[i][] = dp[i-][] + cnt[i] * i;
         dp[i][] = max (dp[i-][], dp[i-][]);
         ret = max (ret, dp[i][]);
         ret = max (ret, dp[i][]);
     }
     return ret;
 }
 int main(void)      //Codeforces Round #260 (Div. 1) A. Boredom
 {
     int n;    scanf ("%d", &n);
     int mx = ;
     for (int i=; i<=n; ++i)
     {
         int x;  scanf ("%d", &x);    cnt[x]++;
         mx = max (mx, x);
     }
     printf ("%I64d\n", work (mx));
     return ;
 }