Stall Reservations Page43 贪心+优先队列

Stall Reservations Page43 贪心+优先队列

题意：给出N个区间，将其不重叠地放在数轴上，至少需要几个数轴？ [1, 2]，[2, 3]算作重叠

贪心思想：将区间左端点从小到大排序，在遍历的同时，用优先队列记录下当前所有数轴的最小右端点，如果该区间能放进其中一个数轴，就放进去，并修改最右端点，如果放不进去，那么就新建一个数轴

代码：

#include<cstdio>
#include<cstring>
#include<algorithm>
#include<iostream>
#include<string>
#include<vector>
#include<stack>
#include<bitset>
#include<cstdlib>
#include<cmath>
#include<set>
#include<list>
#include<deque>
#include<queue>
#include<map>
#define ll long long
#define pb push_back
#define rep(x,a,b) for (int x=a;x<=b;x++)
#define repp(x,a,b) for (int x=a;x<b;x++)
#define W(x) printf("%d\n",x)
#define WW(x) printf("%lld\n",x)
#define pi 3.14159265358979323846
#define mem(a,x) memset(a,x,sizeof a)
#define lson rt<<1,l,mid
#define rson rt<<1|1,mid+1,r
using namespace std;
const int maxn=2e6+7;
const int INF=1e9;
const ll INFF=1e18;
int ans[maxn],m=0,n;
struct node
{
    int l,r,id;
    bool operator<(const node &x)const
    {
        return r>x.r;
    }
}p[maxn];
bool cmp(node a,node b)
{
    if (a.l==b.l)return a.r<b.r;
    else return a.l<b.l;
}
priority_queue<node> Q;
int main()
{
    scanf("%d",&n);
    rep(i,1,n)
    {
        scanf("%d%d",&p[i].l,&p[i].r);
        p[i].id=i;
    }
    sort(p+1,p+1+n,cmp);
    rep(i,1,n)
    {
        if (Q.empty())
        {
            Q.push(p[i]);
            ans[p[i].id]=++m;
            continue;
        }
        node u=Q.top();
        if (p[i].l>u.r)
        {
            Q.pop();
            Q.push(p[i]);
            ans[p[i].id]=ans[u.id];
        }
        else
        {
            Q.push(p[i]);
            ans[p[i].id]=++m;
        }
    }
    W(m);rep(i,1,n)W(ans[i]);
    return 0;
}