codeforces - 789C 【分类+简单递推】

#include <bits/stdc++.h>
#define rep(i,a,b) for(int i = a;i <= b;++ i)
#define per(i,a,b) for(int i = a;i >= b;-- i)
#define mem(a,b) memset((a),(b),sizeof((a)))
#define FIN freopen("in.txt","r",stdin)
#define IO ios_base::sync_with_stdio(0),cin.tie(0)
#define pb push_back
#define mid ((l+r)>>1)
#define ls (id<<1)
#define rs ((id<<1)|1)
using namespace std;
typedef long long LL;
typedef pair<int, LL> PIR;
const int N = 1e5+5;

int n;
LL a[N], sum1[N], sum2[N];

int main()
{IO;
    //FIN;
    cin >> n;
    rep(i, 1, n)    cin >> a[i];
    rep(i, 1, n-1)  sum1[i] = sum1[i-1]+abs(a[i+1]-a[i])*((i-1)&1?-1:1);
    rep(i, 1, n-1)  sum2[i] = sum2[i-1]+abs(a[i+1]-a[i])*((i-1)&1?1:-1);
    LL ans = -1e9, minn = 1e9;
    rep(i, 1, n-1){
        ans = max(ans, max(sum1[i], sum1[i]-minn));
        minn = min(minn, sum1[i]);
    }
    minn = 1e9;
    rep(i, 1, n-1){
        ans = max(ans, max(sum2[i], sum2[i]-minn));
        minn = min(minn, sum2[i]);
    }
    cout << ans << endl;
    return 0;
}