存一个网络流模板

#include<iostream>
#include<cstdio>
#include<cstring>
#include<queue>
using namespace std;
int point[2100], next[2000003], v[2000003], remain[2000003];
int deep[2100], cur[2100], num[2100], n, m, tot, ans, laste[2100];
int a[2100], f[2100];
const int inf = 1e9;
void add(int x, int y, int z)
{
    tot++; next[tot] = point[x]; point[x] = tot; v[tot] = y; remain[tot] = z;
    tot++; next[tot] = point[y]; point[y] = tot; v[tot] = x; remain[tot] = 0;
}
int adde(int s, int t)
{
    int now = t, minn = inf;
    while (now != s)
    {
        minn = min(minn, remain[laste[now]]);
        now = v[laste[now] ^ 1];
    }
    now = t;
    while (now != s)
    {
        remain[laste[now]] -= minn;
        remain[laste[now] ^ 1] += minn;
        now = v[laste[now] ^ 1];
    }
    return minn;
}
void bfs(int s, int t)
{
    for (int i = s; i <= t; i++)
        deep[i] = t + 2;
    deep[t] = 0;
    queue<int> p;
    p.push(t);
    while (!p.empty())
    {
        int now = p.front(); p.pop();
        for (int i = point[now]; i != -1; i = next[i])
            if (deep[v[i]] == t + 2 && remain[i ^ 1])
            {
                deep[v[i]] = deep[now] + 1;
                p.push(v[i]);
            }
    }
}
int isap(int s, int t)
{
    int flow = 0, now = s;
    bfs(s, t);
    memset(num, 0, sizeof(num));
    for (int i = s; i <= t; i++)  num[deep[i]]++;
    for (int i = s; i <= t; i++)  cur[i] = point[i];
    while (deep[s] <= t)
    {
        if (now == t)
        {
            flow += adde(s, t);
            now = s;
        }
        bool hasfind = false;
        for (int i = cur[now]; i != -1; i = next[i])
        {
            if (deep[v[i]] + 1 == deep[now] && remain[i])
            {
                hasfind = true;
                cur[now] = i;
                laste[v[i]] = i;
                now = v[i];
                break;
            }
        }
        if (!hasfind)
        {
            int minn = t;
            for (int i = point[now]; i != -1; i = next[i])
                if (remain[i])
                    minn = min(minn, deep[v[i]] + 1);
            if (!--num[deep[now]]) break;
            deep[now] = minn;
            num[minn]++; cur[now] = point[now];
            if (now != s)
                now = v[laste[now] ^ 1];
        }
    }
    return flow;
}
void solve1()
{
    for (int i = 1; i <= n; i++)
    {
        if (f[i] == 1)  add(0, i, 1);
        if (f[i] == ans) add(i + n, 2 * n + 1, 1);
        add(i, i + n, 1);
    }
    for (int i = 2; i <= n; i++)
    {
        for (int j = 1; j < i; j++)
            if (f[i] == f[j] + 1 && a[i] >= a[j])
                add(j + n, i, 1);
    }
    if (ans == 1) printf("%d\n", n);
    else
        printf("%d\n", isap(0, 2 * n + 1));
}
void solve2()
{
    tot = -1; memset(next, -1, sizeof(next)); memset(point, -1, sizeof(point));
    for (int i = 1; i <= n; i++)
    {
        int v = 1;
        if (i == 1 || i == n) v = inf;
        if (f[i] == 1) add(0, i, v);
        if (f[i] == ans) add(i + n, 2 * n + 1, v);
        add(i, i + n, v);
    }
    for (int i = 2; i <= n; i++)
    {
        for (int j = 1; j < i; j++)
            if (f[i] == f[j] + 1 && a[i] >= a[j])
                add(j + n, i, 1);
    }
    if (ans == 1) printf("%d\n", n);
    else
        printf("%d\n", isap(0, 2 * n + 1));
}
int main()
{
    tot = -1; memset(next, -1, sizeof(next)); memset(point, -1, sizeof(point));
    scanf("%d", &n);
    for (int i = 1; i <= n; i++) scanf("%d", &a[i]);
    f[1] = 1;
    for (int i = 2; i <= n; i++)
    {
        for (int j = 1; j < i; j++)
            if (f[i] < f[j] && a[j] <= a[i])
                f[i] = f[j];
        f[i]++;
    }
    ans = 0;
    for (int i = 1; i <= n; i++)
        ans = max(ans, f[i]);
    printf("%d\n", ans);
    solve1();
    solve2();
}