HDU 3265 posters (Scan Line)

Link: HDU 3265 posters

Given n rectangles, which are special, are all removed and the last Covered Area of the image is asked.

Solution: At the beginning, I thought it would be better to directly scan the line. One was added and the other was reduced, but I couldn't run the samples after writing, I still do not have a deep understanding of the scanning line, because the scanning line does not have a Pushdown operation, because it must have a reduction in each segment, so if it is a reduction at the beginning, it cannot be done.
The positive solution is to divide a graph into four smaller Rectangles and then scan the line directly.

#include <cstdio>#include <cstring>#include <vector>#include <algorithm>using namespace std;const int maxn = 50005;#define lson(x) ((x)<<1)#define rson(x) (((x)<<1)|1)int lc[maxn << 2], rc[maxn << 2], v[maxn << 2], s[maxn << 2];inline void pushup (int u) {    if (v[u])        s[u] = rc[u] - lc[u] + 1;    else if (rc[u] == lc[u])        s[u] = 0;    else        s[u] = s[lson(u)] + s[rson(u)];}inline void maintain (int u, int d) {    v[u] += d;    pushup(u);}void build (int u, int l, int r) {    lc[u] = l;    rc[u] = r;    s[u] = v[u] = 0;    if (l == r)        return ;    int mid = (l + r) / 2;    build(lson(u), l, mid);    build(rson(u), mid + 1, r);    pushup(u);}void modify (int u, int l, int r, int d) {    if (l <= lc[u] && rc[u] <= r) {        maintain(u, d);        return;    }    int mid = (lc[u] + rc[u]) / 2;    if (l <= mid)        modify(lson(u), l, r, d);    if (r > mid)        modify(rson(u), l, r, d);    pushup(u);}struct Seg {    int x, l, r, d;    Seg (int x = 0, int l = 0, int r = 0, int d = 0) {        this->x = x;        this->l = l;        this->r = r;        this->d = d;    }};typedef long long ll;int N;vector<Seg> vec;inline bool cmp (const Seg& a, const Seg& b) {        return a.x < b.x;}inline void add (int x1, int y1, int x2, int y2) {    if (y1 == y2 || x1 == x2)        return;    vec.push_back(Seg(x1, y1, y2 - 1, 1));    vec.push_back(Seg(x2, y1, y2 - 1, -1));}void init () {    int x1, x2, x3, x4;    int y1, y2, y3, y4;    scanf("%d%d%d%d", &x1, &y1, &x2, &y2);    scanf("%d%d%d%d", &x3, &y3, &x4, &y4);    add (x1, y1, x2, y3);    add (x1, y3, x3, y4);    add (x4, y3, x2, y4);    add (x1, y4, x2, y2);}int main () {    while (scanf("%d", &N) == 1 && N) {        build(1, 0, 50000);        vec.clear();        for (int i = 0; i < N; i++)            init();        sort(vec.begin(), vec.end(), cmp);        ll ans = 0;        for (int i = 0; i < vec.size(); i++) {            modify(1, vec[i].l, vec[i].r, vec[i].d);            if (i != vec.size() - 1)                ans += 1LL * s[1] * (vec[i+1].x - vec[i].x);        }        printf("%I64d\n", ans);    }    return 0;}

HDU 3265 posters (Scan Line)