《关于m<=1e4 却可以O(n^2)过这档事》
code:
#include <bits/stdc++.h>
using namespace std;
const int N = 1e4 + 10;
int f[N];
struct node{
    int t, x, y;
}mouse[N];
int n, m;

int main()
{
    ios::sync_with_stdio(false);
    cin.tie(0);
    cout.tie(0);

    cin >> n >> m;
    for(int i = 1;i <= m;i++){
        f[i] = 1;
        int t, x, y;
        cin >> t >> x >> y;
        mouse[i] = {t, x, y};
    }

    for(int i = 1;i <= m;i++){
        for(int j = i - 1;j >= 1;j--){
            auto a = mouse[i], b = mouse[j];
            if(a.t - b.t >= abs(a.x - b.x) + abs(a.y - b.y)){
                f[i] = max(f[i], f[j] + 1);
            }
        }
    }

    int ans = 0;
    for(int i = 1;i <= m;i++){
        ans = max(ans, f[i]);
    }
    cout << ans;
    return 0;
}