uva-10534 Wavio Sequence

#include<iostream>
#include<cstdio>
#include<map>
#include<math.h>
#include<cstring>
#include<algorithm>
#define INF 0x1f1f1f1f
using namespace std;
int main()
{
int n, i, a[10010];
while(scanf("%d",&n) != EOF)
{
for(i = 1; i <= n; i++)
{
scanf("%d",&a[i]);
}
int t1 = 0, t2 = 0;
int dp1[10010], s[10010], dp2[10010];
memset(dp1, 0, sizeof(dp1));
memset(s, -1, sizeof(s));
int top = 0;
s[0] = -INF;
//从前往后求出单调递增子序列
for(i = 1; i <= n; i++)
{
if(a[i] > s[top])
{
s[++top] = a[i];
dp1[i] = top;
}
else
{
int l = 1, r = top;
while(l <= r)
{
int mid = (l + r) / 2;
if(a[i] > s[mid])
{
l = mid + 1;
}
else
r = mid - 1;
}
s[l] = a[i];
dp1[i] = l;
}
if(dp1[i] > t1)
t1 = dp1[i];
}
memset(dp2, 0, sizeof(dp2));
memset(s, -1, sizeof(s));
top = 0;
s[0] = -INF;
//从后往前求出单调递增子序列
for(i = n; i > 0; i--)
{
if(a[i] > s[top])
{
s[++top] = a[i];
dp2[i] = top;
}
else
{
int l = 1, r = top;
while(l <= r)
{
int mid = (l + r) / 2;
if(a[i] > s[mid])
{
l = mid + 1;
}
else
r = mid - 1;
}
s[l] = a[i];
dp2[i] = l;
}
if(dp2[i] > t2)
t2 = dp2[i];
}
int ans = 1,tem;
//每次求最小值
for(int i = 1;i <= n;i++)
{
tem = min(dp1[i],dp2[i]);
ans = max(tem*2-1,ans);
}
cout << ans << endl;

}
return 0;
}