codeforces - 789C 分类+简单递推

Posted 2020-09-07 NWU_ACM

 1 #include <bits/stdc++.h>
 2 #define rep(i,a,b) for(int i = a;i <= b;++ i)
 3 #define per(i,a,b) for(int i = a;i >= b;-- i)
 4 #define mem(a,b) memset((a),(b),sizeof((a)))
 5 #define FIN freopen("in.txt","r",stdin)
 6 #define IO ios_base::sync_with_stdio(0),cin.tie(0)
 7 #define pb push_back
 8 #define mid ((l+r)>>1)
 9 #define ls (id<<1)
10 #define rs ((id<<1)|1)
11 using namespace std;
12 typedef long long LL;
13 typedef pair<int, LL> PIR;
14 const int N = 1e5+5;
15 
16 int n;
17 LL a[N], sum1[N], sum2[N];
18 
19 int main()
20 {IO;
21     //FIN;
22     cin >> n;
23     rep(i, 1, n)    cin >> a[i];
24     rep(i, 1, n-1)  sum1[i] = sum1[i-1]+abs(a[i+1]-a[i])*((i-1)&1?-1:1);
25     rep(i, 1, n-1)  sum2[i] = sum2[i-1]+abs(a[i+1]-a[i])*((i-1)&1?1:-1);
26     LL ans = -1e9, minn = 1e9;
27     rep(i, 1, n-1){
28         ans = max(ans, max(sum1[i], sum1[i]-minn));
29         minn = min(minn, sum1[i]);
30     }
31     minn = 1e9;
32     rep(i, 1, n-1){
33         ans = max(ans, max(sum2[i], sum2[i]-minn));
34         minn = min(minn, sum2[i]);
35     }
36     cout << ans << endl;
37     return 0;
38 }

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