Luogu1856 [USACO5.5] Picture rectangular perimeter (scan line segment tree)

For the horizontal axis, with the difference with the previous scan; for vertical axis, with a height difference does not intersect with the line segment \ (* 2 \) of product;
difficulties in pushdown, taking care to maintain covering relation. Then pay attention to negative

#include <iostream>
#include <cstdio>
#include <cstring>
#include <algorithm>
#include <cmath>
#define R(a,b,c) for(register int  a = (b); a <= (c); ++ a)
#define nR(a,b,c) for(register int  a = (b); a >= (c); -- a)
#define Max(a,b) ((a) > (b) ? (a) : (b))
#define Min(a,b) ((a) < (b) ? (a) : (b))
#define Fill(a,b) memset(a, b, sizeof(a))
#define Abs(a) ((a) < 0 ? -(a) : (a))
#define Swap(a,b) a^=b^=a^=b
#define ll long long

#define ON_DEBUG

#ifdef ON_DEBUG

#define D_e_Line printf("\n\n----------\n\n")
#define D_e(x)  cout << #x << " = " << x << endl
#define Pause() system("pause")

#else

#define D_e_Line ;

#endif

struct ios{
    template<typename ATP>ios& operator >> (ATP &x){
        x = 0; int f = 1; char c;
        for(c = getchar(); c < '0' || c > '9'; c = getchar()) if(c == '-')  f = -1;
        while(c >= '0' && c <= '9') x = x * 10 + (c ^ '0'), c = getchar();
        x*= f;
        return *this;
    }
}io;
using namespace std;

#define lson rt << 1, l, mid
#define rson rt << 1 | 1, mid + 1, r

const int N = 20007;

struct Line{
    int l, r, h, tag;
    
    bool operator < (const Line &com)const{
        if(h != com.h) return h < com.h;
        return tag > com.tag;
    }
}a[N];
struct Tree{
    int sum, num, len, ltag, rtag;
}t[N << 2];

inline void Pushdown(int rt, int l, int r){
    if(t[rt].sum){
        t[rt].num = 1;
        t[rt].len = r - l + 1;
        t[rt].ltag = t[rt].rtag = 1;
        return;
    }
    if(l == r){
        t[rt].len = 0;
        t[rt].num = 0;
        t[rt].ltag = t[rt].rtag = 0;
        return;
    }
    t[rt].len = t[rt << 1].len + t[rt << 1 | 1].len;
    t[rt].num = t[rt << 1].num + t[rt << 1 | 1].num;
    if(t[rt << 1].rtag && t[rt << 1 | 1].ltag) --t[rt].num;
    t[rt].ltag = t[rt << 1].ltag;
    t[rt].rtag = t[rt << 1 | 1].rtag;
}
inline void Updata(int rt, int l, int r, int L, int R, int w){
    if(L <= l && r <= R){
        t[rt].sum += w;
        Pushdown(rt, l, r);
        return;
    }
    int mid = (l + r) >> 1;
    if(L <= mid) Updata(lson, L, R, w);
    if(R > mid)  Updata(rson, L, R, w);
    Pushdown(rt, l, r);
}
int main(){
    int n, m = 0;
    io >> n;
    int maxx = 0xcfcfcfcf, minn = 0x7fffffff;
    R(i,1,n){
        int X1, Y1, X2, Y2;
        io >> X1 >> Y1 >> X2 >> Y2;
        maxx = Max(maxx, X2);
        minn = Min(minn, X1);
        a[++m] = (Line){X1, X2, Y1, 1};
        a[++m] = (Line){X1, X2, Y2, -1};
    }
    if(minn <= 0){
        R(i,1,m){
            a[i].l -= minn - 1;
            a[i].r -= minn - 1;
        }
        maxx -= minn - 1;
    }
    sort(a + 1, a + m + 1);
    int ans = 0, last = 0;
    R(i,1,m){
        Updata(1, 1, maxx, a[i].l, a[i].r - 1, a[i].tag);
        while(a[i].h == a[i + 1].h && a[i].tag == a[i + 1].tag){
            ++i;
            Updata(1, 1, maxx, a[i].l, a[i].r - 1, a[i].tag);
        }
        ans += Abs(t[1].len - last) + (t[1].num * (a[i + 1].h - a[i].h) << 1);
        
        last = t[1].len;        
    }
    printf("%d\n",ans);
    return 0;
}