題意：

略。

題解：

每個點一個線段樹，來優化DP。

用線段樹動態開點。

然而這裡學到了一個技巧：用map陣列模擬二維陣列，達到動態開點的效果，然後用樹狀陣列求1-n最大值即可。

複雜度O(nlog^2n)，也可以用unordered_map加速。

程式碼：

#include <bits/stdc++.h>
#ifdef LOCAL
#define debug(x) cout<<#x<<" = "<<(x)<<endl;
#else
#define debug(x) 1;
#endif

#define chmax(x,y) x=max(x,y)
#define chmin(x,y) x=min(x,y)
#define lson id<<1,l,mid
#define rson id<<1|1,mid+1,r
#define lowbit(x) x&-x
#define mp make_pair
#define pb push_back
#define fir first
#define sec second
using namespace std;
typedef long long ll;
typedef unsigned long long ull;
typedef pair<int, int> pii;

const int MOD = 1e9 + 7;
const double PI = acos (-1.);
const double eps = 1e-10;
const int INF = 0x3f3f3f3f;
const ll INFLL = 0x3f3f3f3f3f3f3f3f;
const int MAXN = 5e5 + 5;

unordered_map<int, int> tree[MAXN];
int query (int x, int id) {
    int ret = 0;
    while (x) {
        ret = max(ret, tree[id][x]);
        x -= lowbit(x);
    }
    return ret;
}

void add (int x, int id, int v) {
    while (x <= 100001) {
        tree[id][x] = max(tree[id][x], v);
        x += lowbit(x);
    }
}



int main() {
#ifdef LOCAL
    freopen ("input.txt", "r", stdin);
#endif
    int n, m;
    int ans = 0;
    scanf ("%d %d", &n, &m);
    for (int i = 1; i <= m; i++) {
        int a, b, w;
        scanf ("%d %d %d", &a, &b, &w);
        w++;
        int ret = 0;
        ans = max(ans, ret = query(w - 1, a) + 1);
        add(w, b, ret);
    }
    printf ("%d\n", ans);
    return 0;
}