CodeForces 788A - Functions again [ DP ]

反着求一遍最大连续子序列(前项依赖)

 

 1 #include <bits/stdc++.h>
 2 using namespace std;
 3 #define LL long long
 4 const int MAXN = 200005;
 5 int n;
 6 LL dp[MAXN];
 7 LL a[MAXN];
 8 LL Cal(int i)
 9 {
10     return abs(a[i] - a[i+1]);
11 }
12 int main()
13 {
14     scanf("%d", &n);
15     for (int i = 1; i <= n; i++)
16         scanf("%lld", &a[i]);
17     memset(dp, 0, sizeof(dp));
18     dp[n-1] = Cal(n-1);
19     LL ans = dp[n-1];
20     for (int i = n-2; i > 0; i--)
21     {
22         dp[i] = max(Cal(i), Cal(i) - dp[i+1]);
23         if (i < n-2)
24             dp[i] = max(dp[i], dp[i+2] - Cal(i+1) + Cal(i) );
25         ans = max(dp[i], ans);
26     }
27     printf("%lld\n", ans);
28 }