luogu 1280

f[i]

对于某个区间起点，状态转移到终点，要反过来枚举 i 

方程不难想,两种情况

f[i] =max{ f[i+len[j] ] } 

 f[i]= f[i+1]+1

#include <iostream>
#include <algorithm>
#include <cmath>
using namespace std ;
 const int N=1e4+3;
 int n,m,b[N],f[N];
 
 struct T{
 	int x,l;
 	bool operator<(T a)const{
 		return x>a.x;
	 }
 }a[N];
 

 int solve(){
 	int i,j;
 	int x=1;
 	for(i=n;i>=1;i--)
 	 if(b[i]){
 	 	for(j=1;j<=b[i];j++)
 	 	 f[i]=max(f[i],f[i+a[x].l]),x++;
	  }
 	 else f[i]=f[i+1]+1;
 }

 signed main(){
 	int i;
 	cin>>n>>m;
 	for(i=1;i<=m;i++) 
	 cin>>a[i].x>>a[i].l,b[a[i].x]++;
 	sort(a+1,a+1+m);
 	solve();
 	cout<<f[1];
 }