萌新刚学 OI，再次求助挂掉的网络流

#include <iostream> 
#include <cstring>
#include <queue>
#define MAXN 300000
#define INF 0x7f7f7f7f
#define QWQ cout << "QWQ" << endl;
using namespace std;
int tot = 1, n, m, s, t;
int max(int x, int y) {return ((x > y) ? (x) : (y));}
int min(int x, int y) {return ((x < y) ? (x) : (y));}
struct node {
    int to, val, next;
} gra[MAXN * 2 + 10];
int head[MAXN + 10], fa[MAXN + 10];
void link(int x, int y, int z) {
    gra[++tot].to = y, gra[tot].val = z, gra[tot].next = head[x], head[x] = tot;
    gra[++tot].to = x, gra[tot].val = 0, gra[tot].next = head[y], head[y] = tot;
}
int dis[MAXN + 10], f[MAXN + 10], Now[MAXN + 10], a[MAXN + 10];
bool vis[MAXN + 10];
bool qwq[MAXN + 10];
bool bfs() {
    memset(dis, 0, sizeof(dis));
    queue <int> que;
    que.push(s), dis[s] = 1, Now[s] = head[s];
    while(!que.empty()) {
        int fr = que.front(); que.pop();
        for(int p = head[fr]; p; p = gra[p].next) {
            int v = gra[p].to, w = gra[p].val;
            if(w && !dis[v]) {
                que.push(v);
                Now[v] = head[v];
                dis[v] = dis[fr] + 1;
                if(v == t) return 1;
            }
        }
    }
    return 0;
}
int Dinic(int u, int over) {
    if(u == t) return over;
    int res = over;
    for(int p = Now[u]; p && res; p = gra[p].next) {
        int v = gra[p].to, w = gra[p].val;
        Now[u] = p;
        if(w && dis[v] == dis[u] + 1) {
            int k = Dinic(v, min(res, w));
            if(!k) dis[v] = 0x7f7f7f7f;
            if(u != s) vis[v - n] = 1;
            gra[p].val -= k;
            gra[p ^ 1].val += k;
            res -= k;
        }
    }
    return over - res;
}
int Max_Flow() {
    int rest = 0;
    while(bfs()) {
        rest += Dinic(s, INF);
    }
    return rest;
}
int solve_1(int len) {
    for(int p = 1; p <= len; p++) f[p] = 1;
    for(int p = 1; p <= len; p++)
        for(int i = 1; i < p; i++)
            if(a[p] >= a[i])
                f[p] = max(f[p], f[i] + 1);
    int maxn = 0;
    for(int p = 1; p <= len; p++)
        maxn = max(maxn, f[p]);
    return maxn;
}
void solve_2(int len, int ml) {
    for(int p = 1; p <= len; p++) {
        if(f[p] == 1) link(s, p, 1);
        if(f[p] == ml) link(p + len, t, 1);
        link(p, p + len, 1);
    }
    for(int p = 1; p <= len; p++)
        for(int i = 1; i < p; i++)
            if(f[i] + 1 == f[p] && a[p] >= a[i])
                link(i + len, p, 1);
    int qwq = Max_Flow();
    cout << qwq << endl;
}
void solve_3(int len, int ml) {
    link(1, 1 + len, INF), link(s, 1, INF);
    if(f[len] == ml) link(len, len + len, INF), link(len + len, t, INF);
    cout << Max_Flow() << endl;
}
int main() {
    int n;
    cin >> n, s = n * 2 + 1, t = n * 2 + 2;
    for(int p = 1; p <= n; p++)
        cin >> a[p];
    int ml = solve_1(n);
    cout << ml << endl;
    solve_2(n, ml);
    solve_3(n, ml); 
}

我也不知道第三问怎么会挂啊/kk
检查了很多次，没毛病啊/kk 求助/kel