合唱队形

 

传送门：https://www.luogu.org/problemnew/show/P1091

正反各求一遍最长上升子序列，然后相加求最大值

#include<cstdio>
#include<algorithm> 
using namespace std;
inline int read()
{
    static char ch;
    while((ch = getchar()) < '0' || ch > '9');
    int ret = ch -48;
    while((ch = getchar()) >= '0' && ch <= '9')
        ret = ret * 10 + ch - 48;
    return ret;
}
int n,a[105],f1[105],f2[105],ans;
int main()
{
    n = read();
    for(int i = 1;i <= n;i++) a[i] = read();
    a[0] = a[n+1] = 0;
    for(int i = 1;i <= n;i++)
        for(int j = 0;j < i;j++)
            if(a[i] > a[j])
                f1[i] = max(f1[i] ,f1[j] + 1);
    for(int i = n;i > 0;i--)
        for(int j = n+1;j > i;j--)
            if(a[i] > a[j])
                f2[i] = max(f2[i],f2[j]+1);
    for(int i = 1;i <= n;i++)
        ans = max(f1[i]+f2[i]-1,ans);    //重叠的要减掉
    printf("%d\n",n-ans);
    return 0;
}