1427C - The Hard Work of Paparazzi - CodeForces Solution

//jiudge: 26921: 1687360739
#include<bits/stdc++.h>

using namespace std;
typedef long long LL;
const int N = 1e5+10;
int dp[N];
struct xx {
	int t, x, y;
}a[N];
int dis(xx a1, xx a2) {
	return abs(a1.x-a2.x)+abs(a1.y-a2.y);
}
int main() {
	memset(dp, -1, sizeof dp);
	int r, n;
	scanf("%d%d", &r, &n);
	a[0].x = 1, a[0].y = 1; dp[0] = 0;
	for(int i = 1; i <= n; ++i) scanf("%d%d%d", &a[i].t, &a[i].x, &a[i].y);
	for(int i = 1; i <= n; ++i) {
		for(int j = max(0, i-1-r*4); j < i; ++j) {
			if(dp[j] != -1 && a[i].t - a[j].t >= dis(a[i], a[j])) 
				dp[i] = max(dp[i], dp[j]+1);
		}
	}
	int ans = 0;
	for(int i = 1; i <= n; ++i) ans = max(ans, dp[i]);
	printf("%d\n", ans);
	return 0;
}