题目

代码

左端点排序+区间合并

#include <bits/stdc++.h>
using namespace std;
#define null -0x3f3f3f3f
#define x first
#define y second
typedef pair<int, int> PII;
const int N = 1e5+10;
vector<PII> v;
int main()
{
    int n;
    cin >> n;
    for(int i = 1; i <= n; i++)
    {
        int l, r;
        cin >> l >> r;
        v.push_back({l,r});
    }
    
    sort(v.begin(), v.end());
    
    int ans = 0;
    int l = null, r = null;
    for(auto c : v)
    {
        int x = c.x, y = c.y;
        if(l == null) l = x, r = y;
        else
        {
            if(x > r) ans++, l = x, r = y;
            else if(y > r) l = x;
            else l = x, r = y;
        }
    }
    
    ans += 1;
    
    cout << ans;
}

 右端点排序+贪心

#include <bits/stdc++.h>
using namespace std;
#define null -0x3f3f3f3f
#define x first
#define y second
typedef pair<int, int> PII;
const int N = 1e5+10;
vector<PII> v;
int main()
{
    int n;
    cin >> n;
    for(int i = 1; i <= n; i++)
    {
        int l, r;
        cin >> l >> r;
        v.push_back({r, l});
    }
    
    sort(v.begin(), v.end());
    
    int ans = 1;
    int end = v[0].x;
    for(auto c : v)
    {
        int l = c.y, r = c.x;
        if(l > end) end = r, ans++;
    }
    
    cout << ans;
}