• 链接：https://www.acwing.com/problem/content/484/

算法

序列为先上升后下降，登山问题的对偶问题。

代码

#include <iostream>
using namespace std;

const int N = 110;
int n, w[N], f[N], g[N];

int main() {
    cin >> n;
    for (int i = 1; i <= n; ++i) cin >> w[i];
    int ans = 0;
    for (int i = 1; i <= n; ++i) {
        f[i] = 1;
        for (int j = 1; j < i; ++j) {
            if (w[i] > w[j]) f[i] = max(f[i], f[j] + 1);
        }
    }
    
    for (int i = n; i ; --i) {
        g[i] = 1;
        for (int j = n; j > i; --j) {
            if (w[i] > w[j]) g[i] = max(g[i], g[j] + 1);
        }
    }
    
    for (int i = 1; i <= n; ++i) ans = max(ans, f[i] + g[i] - 1);
    cout << n -  ans << endl;
    return 0;
}

Acwing-----482. 合唱队形