CodeForces 788A

反着求一遍最大连续子序列(前项依赖)

#include <bits/stdc++.h>
using namespace std;
#define LL long long
const int MAXN = 200005;
int n;
LL dp[MAXN];
LL a[MAXN];
LL Cal(int i)
{
    return abs(a[i] - a[i+1]);
}
int main()
{
    scanf("%d", &n);
    for (int i = 1; i <= n; i++)
        scanf("%lld", &a[i]);
    memset(dp, 0, sizeof(dp));
    dp[n-1] = Cal(n-1);
    LL ans = dp[n-1];
    for (int i = n-2; i > 0; i--)
    {
        dp[i] = max(Cal(i), Cal(i) - dp[i+1]);
        if (i < n-2)
            dp[i] = max(dp[i], dp[i+2] - Cal(i+1) + Cal(i) );
        ans = max(dp[i], ans);
    }
    printf("%lld
", ans);
}