$虽然数据有点搞，但是终于AC了2333$

离散化+简单DP+线段树

#include<bits/stdc++.h>
#define x first
#define y second
using namespace std;

typedef pair<int,int>PII;
const int N=6e5+7;

int n,m;
vector<PII>v[N];
bool vis[N<<1];

struct node
{
    int l,r;
    PII val;
    PII lazy;
}tr[N<<2];

void pushup(int u)
{
    tr[u].val=max(tr[u<<1].val,tr[u<<1|1].val);
}


void pushdown(int u)
{
    if(tr[u].lazy.y==-1)return ;
    auto &root=tr[u],&left=tr[u<<1],&right=tr[u<<1|1];

    left.lazy =max(root.lazy, left.lazy), left.val =max(left.val,root.lazy);
    right.lazy=max(root.lazy,right.lazy),right.val=max(right.val,root.lazy);
    root.lazy={0,-1};
}

void build(int u,int l,int r)
{
    if(l==r)tr[u]={l,r,{0,-1},{0,-1}};
    else
    {
        tr[u]={l,r};
        int mid=l+r>>1;
        build(u<<1,l,mid),build(u<<1|1,mid+1,r);
        pushup(u);
    }
}

void modify(int u,int l,int r,PII d)
{
    if(tr[u].l>=l&&tr[u].r<=r)
        tr[u].lazy=max(tr[u].lazy,d),tr[u].val=max(tr[u].val,d);
    else
    {
        pushdown(u);
        int mid=tr[u].l+tr[u].r>>1;
        if(l<=mid)modify(u<<1,l,r,d);
        if(r>mid)modify(u<<1|1,l,r,d);
        pushup(u);
    }
}

PII query(int u,int l,int r)
{
    if(tr[u].l>=l&&tr[u].r<=r)return tr[u].val;
    pushdown(u);
    PII res={0,-1};
    int mid=tr[u].l+tr[u].r>>1;
    if(l<=mid)res=max(query(u<<1,l,r),res);
    if(r>mid)res=max(query(u<<1|1,l,r),res);
    return res;
}

int main()
{
    ios::sync_with_stdio(false);
    cin.tie(NULL),cout.tie(NULL);
    cin>>n>>m;
    vector<int>nums;
    while(m--)
    {
        int x,l,r;
        cin>>x>>l>>r;
        v[x].push_back({l,r});
        nums.push_back(l),nums.push_back(r);
    }
    //离散化
    sort(nums.begin(),nums.end());
    nums.erase(unique(nums.begin(),nums.end()),nums.end());
    int sizes=nums.size();

    for (int i = 1; i <= n; i++)
        for (auto& it : v[i]) {
            it.x = upper_bound(nums.begin(),nums.end(), it.x) - nums.begin();
            it.y = upper_bound(nums.begin(),nums.end(), it.y) - nums.begin();
        }

    build(1,1,sizes);
    //记录前驱
    vector<int>pre(n+1,-1);
    //DP
    for(int i=1;i<=n;i++)
    {
        PII mx={0,-1};
        for(auto &it:v[i])
            mx=max(mx,query(1,it.x,it.y));
        pre[i]=mx.y;
        mx.x++;
        mx.y=i;
        for(auto &it:v[i])
            modify(1,it.x,it.y,mx);
    }
    //求最大值
    PII ans=query(1,1,sizes);

    int cur=ans.y;
    while(cur!=-1)
    {
        vis[cur]=true;
        cur=pre[cur];
    }
    cout<<n-ans.x<<endl;
    for(int i=1;i<=n;i++)
        if(!vis[i])
            cout<<i<<' ';

}