HDU 5805 - NanoApe Loves Sequence （BestCoder Round #86）

#include <iostream>
#include <cstdio>
#include <cmath>
using namespace std;
#define LL long long
const int N = 100005;
int t, n, p1, p2, p3;
LL a
;
LL s1
, s2
;
LL sum;
int main()
{
scanf("%d", &t);
while(t--)
{
scanf("%d", &n);
for(int i = 1; i <= n; i++)
scanf("%I64d", &a[i]);
p1 = p2 = p3 = 0;
s1[0] = -1;
for(int i = 1; i < n; i++)
{
s1[i] = abs(a[i + 1] - a[i]);//相邻
if(s1[p1] < s1[i] ) p1 = i;//最大
}
for(int i = 1; i < n; i++)
{
if(i == p1) continue;
else if(s1[p2] < s1[i]) p2 = i;//第二大
}
for(int i = 1; i < n; i++)
{
if(i == p1 || i == p2) continue;//第三大
else if(s1[p3] < s1[i]) p3 = i;
}
for(int i = 2; i < n; i++)
s2[i] = abs(a[i+1] - a[i-1]);//去掉 i 点新增值

sum = 0;
if(p1 == 1) sum += s1[p2];
else sum += s1[p1];
for(int i = 2; i < n; i++)
{
if(p1 == i-1 || p1 == i)
{
if(p2 == i-1 || p2 == i) sum += max(s1[p3], s2[i]);
else sum += max(s1[p2], s2[i]);
}
else sum += max(s1[p1], s2[i]);
}
if(p1 == n - 1) sum += s1[p2];
else sum += s1[p1];
printf("%I64d\n",sum);
}
}