acwing907. 区间覆盖（贪心）

思路

1. 从左向右贪心遇到没覆盖的点就选选段。

代码

#include <bits/stdc++.h>
using namespace std;
#define db  double
#define ll  long long
#define Pir pair<int, int>
#define fi  first
#define se  second
#define pb  push_back
#define m_p make_pair
#define inf 0x3f3f3f3f
#define INF 0x3f3f3f3f3f3f3f3f
/*==========ACMer===========*/
const int N = 1e5 + 10;
Pir p[N];

int main()
{
    
    
    int s, t;
    scanf("%d %d", &s, &t);
    int n; scanf("%d", &n);
    int x, y;
    for (int i = 1; i <= n; i ++)
    {
    
    
        scanf("%d %d", &x, &y);
        p[i] = m_p(x, y);
    }

    sort(p + 1, p + 1 + n);
    int i = 1;
    int ans = 0;
    while (i <= n)
    {
    
    
        int mx = -inf;
        while (i <= n && p[i].fi <= s)
        {
    
    
            mx = max(mx, p[i].se);
            i ++;
        }

        if (mx < s)
        {
    
    
            printf("-1\n");
            return 0;
        }

        s = mx;
        ans ++;

        if (mx >= t)
        {
    
    
            printf("%d\n", ans);
            return 0;
        }
    }

    printf("-1\n");


    return 0;
}