为什么不是背包问题？

#include <iostream>
#include <vector>
#include <algorithm>
using namespace std;
typedef struct Cpet
{
    int s, e;
    Cpet(int s, int e) :s(s), e(e){};
};
int N;
vector<int> best;
vector<Cpet *> cps;
bool comp(Cpet *a, Cpet *b)
{
    if (a->e != b->e)
        return a->s < b->s;
    else
        return a->e < b->e;
}
int max(int a, int b){ return a > b ? a : b; }
int main()
{
    best.resize(1000001, 0);
    cin >> N;
    for (int i = 0; i < N; i++)
    {
        int s, e;
        cin >> s >> e;
        cps.push_back(new Cpet(s, e));
    }
    sort(cps.begin(), cps.end(), comp);
    int last = 0;
    for (int i = 1, j = 0; i < 1000001; i++)
    {
        best[i] = best[i - 1];
        while (j < N && cps[j]->e == i)
        {
            best[i] = max(best[i], best[cps[j]->s] + 1);
            j++;
        }
        last = best[i];
        if (j >= N)
            break;
    }
    cout << last;
    return 0;
}