luoguP5490扫描线

扫描线板子题。注意两倍数组（不太清楚原理）

一位大佬的博客：https://blog.csdn.net/qq_38786088/article/details/78633478，讲的太好了。

#include<iostream>
#include<algorithm>
#include<cstdio>

using namespace std;
typedef long long ll;

const int Maxn = 2e5+10;

ll read(){
    ll ans = 0;char last = ' ',ch = getchar();
    while(ch < '0'||ch > '9')last = ch,ch = getchar();
    while('0' <= ch&&ch <= '9')ans = ans*10+ch-'0',ch = getchar();
    if(last == '-')return -ans;return ans;
}

struct node{
    ll x,y1,y2,k;
    bool operator <(const node& asdf)const{
        return x < asdf.x;
    }
}rem[Maxn<<1];

ll ans,n,tot1,tot2,cnt,x1,y1,x2,y2;
ll pos[Maxn<<1],a[Maxn<<1],cov[Maxn<<2],len[Maxn<<2];

void pushup(ll p,ll s,int t){
    if(cov[p])len[p] = pos[t+1]-pos[s];//??
    else if(s == t)len[p] = 0;
    else len[p] = len[p<<1]+len[p<<1|1];
}

void update(ll L,ll R,ll s,ll t,ll p,ll k){
    if(L <= s&&t <= R){cov[p] += k;pushup(p,s,t);return;}
    ll mid = s+t>>1;
    if(L <= mid)update(L,R,s,mid,p<<1,k);
    if(mid < R)update(L,R,mid+1,t,p<<1|1,k);
    pushup(p,s,t);
}

int main(){
    n = read();
    for(int i = 1;i <= n;i++){
        x1 = read(),y1 = read(),x2 = read(),y2 = read();
        a[++tot1] = y1,a[++tot1] = y2;
        rem[++tot2].x = x1,rem[tot2].y1 = y1,rem[tot2].y2 = y2,rem[tot2].k = 1;
        rem[++tot2].x = x2,rem[tot2].y1 = y1,rem[tot2].y2 = y2,rem[tot2].k = -1;
    }
    sort(a+1,a+tot1+1);
    for(int i = 1;i <= tot1;i++)if(a[i] != a[i-1]||i == 1)pos[++cnt] = a[i];
    sort(rem+1,rem+tot2+1);
    for(int i = 1;i < tot2;i++){
        ll L = lower_bound(pos+1,pos+cnt+1,rem[i].y1)-pos;
        ll R = lower_bound(pos+1,pos+cnt+1,rem[i].y2)-pos;
        update(L,R-1,1,cnt,1,rem[i].k);
        ans += len[1]*(rem[i+1].x-rem[i].x);
    }
    cout << ans;
return 0;
}