482. 合唱队形

题意

略（形成山丘式的队形，最少提几个人）

思路

前后各做一次LIS（必须是dp）

f $i$ 就表示以i为结尾的正序的LIS

g $i$ 就表示以i为结尾的逆序的LIS
*

代码

cpp 复制代码

#include <bits/stdc++.h>
using namespace std;
#define int long long
#undef int

#define SZ(X) ((int)(X).size())
#define ALL(X) (X).begin(), (X).end()
#define IOS                                                                                                            \
    ios::sync_with_stdio(false);                                                                                       \
    cin.tie(nullptr);                                                                                                  \
    cout.tie(nullptr)
#define DEBUG(X) cout << #X << ": " << X << '\n'

const int N = 1e5 + 10, INF = 0x3f3f3f3f;

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

signed main() {
    //freopen("Tests/input_1.txt", "r", stdin);
    IOS;

    int n;
    cin >> n;
    for (int i = 1; i <= n; ++ i) cin >> a[i];


    for (int i = 1; i <= n; ++ i) {
        f[i] = 1;
        for (int j = 1; j < i; ++ j) {
            if (a[j] < a[i]) 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 (a[j] < a[i]) g[i] = max(g[i], g[j] + 1);
    }

    int mx = 0;
    for (int i = 1; i <= n; ++ i) {
        mx = max(mx, f[i] + g[i] - 1);
    }

    cout << n - mx;

    return 0;
}