【UVa】Wavio Sequence（dp）

http://uva.onlinejudge.org/index.php?option=com_onlinejudge&Itemid=8&page=show_problem&problem=1475

正反一次lis然后去min{左，右}*2-1即可

#include <cstdio>

#include <cstring>

#include <cmath>

#include <string>

#include <iostream>

#include <algorithm>

#include <queue>

#include <set>

#include <map>

using namespace std;

typedef long long ll;

#define pii pair<int, int>

#define mkpii make_pair<int, int>

#define pdi pair<double, int>

#define mkpdi make_pair<double, int>

#define pli pair<ll, int>

#define mkpli make_pair<ll, int>

#define rep(i, n) for(int i=0; i<(n); ++i)

#define for1(i,a,n) for(int i=(a);i<=(n);++i)

#define for2(i,a,n) for(int i=(a);i<(n);++i)

#define for3(i,a,n) for(int i=(a);i>=(n);--i)

#define for4(i,a,n) for(int i=(a);i>(n);--i)

#define CC(i,a) memset(i,a,sizeof(i))

#define read(a) a=getint()

#define print(a) printf("%d", a)

#define dbg(x) cout << (#x) << " = " << (x) << endl

#define error(x) (!(x)?puts("error"):0)

#define printarr2(a, b, c) for1(_, 1, b) { for1(__, 1, c) cout << a[_][__]; cout << endl; }

#define printarr1(a, b) for1(_, 1, b) cout << a[_] << '\t'; cout << endl

inline const int getint() { int r=0, k=1; char c=getchar(); for(; c<'0'||c>'9'; c=getchar()) if(c=='-') k=-1; for(; c>='0'&&c<='9'; c=getchar()) r=r*10+c-'0'; return k*r; }

inline const int max(const int &a, const int &b) { return a>b?a:b; }

inline const int min(const int &a, const int &b) { return a<b?a:b; }



const int N=10005;

int n, a[N], g[N], f[N], h[N];



void lis() {

	CC(g, 0x3f);

	for1(i, 1, n) {

		int t=lower_bound(g+1, g+1+i, a[i])-g;

		f[i]=t;

		g[t]=a[i];

	}

	CC(g, 0x3f);

	for3(i, n, 1) {

		int t=lower_bound(g+1, g+1+i, a[i])-g;

		h[i]=t;

		g[t]=a[i];

	}

}



int main() {

	while(~scanf("%d", &n)) {

		for1(i, 1, n) read(a[i]);

		lis();

		int ans=0;

		for1(i, 1, n) ans=max(ans, min(f[i], h[i])*2-1);

		printf("%d\n", ans);

	}

	return 0;

}