[luoguP1410] 子序列（DP）

#include <cstdio>
#include <iostream>
#define N 2001
#define max(x, y) ((x) > (y) ? (x) : (y))

int n, tmp;
int a[N], f[N];

inline int read()
{
	int x = 0, f = 1;
	char ch = getchar();
	for(; !isdigit(ch); ch = getchar()) if(ch == ‘-‘) f = -1;
	for(; isdigit(ch); ch = getchar()) x = (x << 1) + (x << 3) + ch - ‘0‘;
	return x * f;
}

int main()
{
	int i, j;
	while(~scanf("%d", &n))
	{
		for(i = 1; i <= n; i++) a[i] = read();
		for(i = 1; i <= n; i++)
		{
			tmp = 0;
			for(j = i - 1; j >= 1; j--)
				if(a[j] >= a[i])
					tmp = max(tmp, f[j]);
			f[i] = tmp + 1;
			if(f[i] >= 3)
			{
				puts("No!");
				break;
			}	
		}
		if(i > n) puts("Yes!");
	}
	return 0;
}