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最新推荐文章于 2022-09-03 14:04:18 发布

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最新推荐文章于 2022-09-03 14:04:18 发布

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分类专栏：线段树文章标签： insert tree struct

本文链接：https://blog.youkuaiyun.com/taozifish/article/details/7854592

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本文介绍了一种利用线段树进行扫描线算法的方法，通过处理矩形覆盖问题，实现计算特定区域内覆盖值从0变为1的总长度，并详细展示了算法的实现过程。

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分x边和y边两次线段树扫描线，寻找cover值0->1的区域，长度*2即可。

#include <cstdio>
#include <cmath>
#include <cstring>
#include <algorithm>
#include <iostream>
using namespace std;
const int maxn=20005;
const int TT=10000;
int n;
struct rect{
    int x1, y1, x2, y2;
}rec[maxn];
struct node{
    int lef, rig, mid, cover;
}seg[maxn*4];

struct line{
    int x1, x2, y, flag;
}l[maxn];

void make_tree(int num, int lef, int rig){
    seg[num].lef=lef;
    seg[num].rig=rig;
    seg[num].mid=(lef+rig)/2;
    seg[num].cover=0;
    if(lef+1!=rig){
        make_tree(num*2, lef, seg[num].mid);
        make_tree(num*2+1, seg[num].mid, rig);
    }
}

int insert(int num, int lef, int rig, int cover, int f){
    if(seg[num].cover!=-1&&seg[num].lef==lef&&seg[num].rig==rig){
        if(cover==1&&seg[num].cover==0&&f){
            seg[num].cover+=cover;
            return seg[num].rig-seg[num].lef;
        }
        seg[num].cover+=cover;
        return 0;
    }
    if(seg[num].cover>0){
        insert(num*2, seg[num].lef, seg[num].mid, seg[num].cover, 0);
        insert(num*2+1, seg[num].mid, seg[num].rig, seg[num].cover, 0);
        seg[num].cover=-1;
    }
    seg[num].cover=-1;
    if(rig<=seg[num].mid)
        return insert(num*2, lef, rig, cover, f);
    else if(lef>=seg[num].mid)
        return insert(num*2+1, lef, rig, cover, f);
    else {
        return insert(num*2, lef, seg[num].mid, cover, f)+
        insert(num*2+1, seg[num].mid, rig, cover, f);
    }
}

void init(int t){
    for(int i=0; i<n; i++){
        if(t==1){
            l[i*2].x1=rec[i].x1; l[i*2].y=rec[i].y1; l[i*2+1].x2=rec[i].x2;  l[i*2+1].y=rec[i].y2;
        }
        else {
             l[i*2].x1=rec[i].y1; l[i*2].y=rec[i].x1; l[i*2+1].x2=rec[i].y2;  l[i*2+1].y=rec[i].x2;
        }
        l[i*2].x1+=TT; l[i*2].y+=TT; l[i*2+1].x2+=TT; l[i*2+1].y+=TT;
        l[i*2].x2=l[i*2+1].x2;
        l[i*2+1].x1=l[i*2].x1;
        l[i*2].flag=1;
        l[i*2+1].flag=-1;
    }
}
bool cmpy(line l1, line l2){
    return l1.y<l2.y;
}

int solve(){
    int ans=0;
    make_tree(1, 0, TT*2);
    sort(l, l+2*n, cmpy);
    for(int i=0; i<2*n-1; i++){
        ans+=2*insert(1, l[i].x1, l[i].x2, l[i].flag, 1);
    }
    return ans;
}

int main(){
    //freopen("1.txt", "r", stdin);
    while(scanf("%d", &n)!=EOF){
        for(int i=0; i<n; i++)
            scanf("%d%d%d%d", &rec[i].x1, &rec[i].y1, &rec[i].x2, &rec[i].y2);
        init(1);
        int ans=solve();
        init(2);
        ans+=solve();
        printf("%d\n", ans);
    }
    return 0;
}