贪心-区间选点

重点
1. 区间排序
2. start和last用来更新上一个重合区间的左端点和右端点
3. 如果当前的区间的左端点不在重合区间内，上个区间内应该至少放一个点，并同时更新下一个重合区间的端点

#include <iostream>
#include <cstring>
#include <algorithm>
#include <queue>
using namespace std;
const int N = 100010, INF = 0x3f3f3f3f;
typedef pair<int, int> PII;
vector<PII> v;
int n;


int main() {
    cin >> n;
    for (int i = 0; i < n; i++) {
        int a, b;
        cin >> a >> b;
        v.push_back({a, b});
    }
    sort(v.begin(), v.end());
    int start = -INF, last = INF, res = 0;
    for (int i = 0; i < v.size(); i++) {
        //printf("v[%d].first = %d, last = %d\n", i, v[i].first, last);
        if (v[i].first > last) {
            if (last != INF) res++;
            start = v[i].first, last = v[i].second;
        } else {
            start = v[i].first, last = min(last, v[i].second);
        }
    }
    if (last != INF) res++;
    cout << res << endl;
    return 0;
}