HDU 1828 (扫描线)

这个是求矩形并的周长，也用扫描线来搞，但是排序的时候不同于面积，在两条线的高度相同是需要优先把下边放在前面（不然有的横边会被多算）。

#include <cstdio>
#include <cstring>
#include <cmath>
#include <algorithm>
#include <iostream>
using namespace std;
#define maxn 5111
#define pl c<<1
#define pr (c<<1)|1
#define lson tree[c].l,tree[c].mid,c<<1
#define rson tree[c].mid+1,tree[c].r,(c<<1)|1

struct node {
    int l, r, mid;
    int len, cover;
    bool ll, rr; // 区间左端点 右端点是不是被覆盖
    int num; // 连续子区间段数
}tree[21111 << 4];
struct segment {
    int l, r, h, flag;
    bool operator < (segment a) const {
        return h < a.h || (h == a.h && flag > a.flag);
    }
}p[maxn<<1];
int n, cnt;
int a, b, c, d;

void build_tree (int l, int r, int c) {
    tree[c].l = l, tree[c].r = r, tree[c].mid = (l+r)>>1;
    tree[c].len = tree[c].cover = tree[c].ll = tree[c].rr = tree[c].num = 0;
    if (l == r)
        return ;
    build_tree (lson);
    build_tree (rson);
    return ;
}

void push_up (int c) {
    if (tree[c].cover) {
        tree[c].len = tree[c].r - tree[c].l + 1;
        tree[c].num = 1;
        tree[c].ll = tree[c].rr = 1;
        return ;
    }
    else if (tree[c].l == tree[c].r) {
        tree[c].len = tree[c].num = tree[c].ll = tree[c].rr = 0;
    }
    else {
        tree[c].len = tree[pl].len + tree[pr].len;
        tree[c].num = tree[pl].num + tree[pr].num;
        tree[c].ll = tree[pl].ll, tree[c].rr = tree[pr].rr;
        if (tree[pl].rr && tree[pr].ll)
            tree[c].num--;
    }
}

void update (int l, int r, int c, int x, int y, int v) {
    if (l == x && r == y) {
        tree[c].cover += v;
        push_up (c);
        return ;
    }
    if (tree[c].mid >= y)
        update (lson, x, y, v);
    else if (tree[c].mid < x) {
        update (rson, x, y, v);
    }
    else {
        update (lson, x, tree[c].mid, v);
        update (rson, tree[c].mid+1, y, v);
    }
    push_up (c);
}

int main () {
    //freopen ("in", "r", stdin);
    while (scanf ("%d", &n) == 1) {
        cnt = 0;
        for (int i = 1; i <= n; i++) {
            scanf ("%d%d%d%d", &a, &b, &c, &d);
            a += 10000, b += 10000, c += 10000, d += 10000;
            p[cnt].l = a, p[cnt].r = c, p[cnt].h = b, p[cnt].flag = 1, cnt++;
            p[cnt].l = a, p[cnt].r = c, p[cnt].h = d, p[cnt].flag = -1, cnt++;
        }
        sort (p, p+cnt);
        build_tree (0, 20000, 1);
        long long ans = 0;
        for (int i = 0; i < cnt-1; i++) {
            int pre = tree[1].len;
            update (0, 20000, 1, p[i].l, p[i].r-1, p[i].flag);
            ans += abs (tree[1].len - pre) + 2 * (long long)tree[1].num * (p[i+1].h - p[i].h);
        }
        int pre = tree[1].len;
        update (0, 20000, 1, p[cnt-1].l, p[cnt-1].r-1, p[cnt-2].flag);
        ans += abs (tree[1].len - pre);
        printf ("%lld\n", ans);
    }
    return 0;
}