hdu1828&poj1177(线段树求矩形交周长，扫描线)

来源：互联网发布：linux系统的命令编辑：程序博客网时间：2024/05/21 07:46
题目链接：hdu1828 poj1177
这篇博客讲的比较好理解：Click
/*hdu 矩形周长，扫描线*/#include<cstdio>#include<cstring>#include<algorithm>using namespace std;#define lson rt<<1#define rson rt<<1|1const int N = 5010;int x[N<<1];struct node{    int l,r,cov;    bool lseg,rseg;//表示某个区间最左边和最右边是否有下底边多于上底边    int sum;//下底边的长度    int segnum;//没有被覆盖的竖边的个数}s[N<<2];struct seg{    int l, r, h, c;    seg(){}    seg(int x1, int x2, int y, int cc):l(x1),r(x2),h(y),c(cc){}    bool operator < (const seg &cmp) const{        if(h == cmp.h) return c > cmp.c;//这里一定不能去掉,比如这组数据:2 0 0 4 4 0 4 4 8        return h < cmp.h;    }}ss[N<<1];void pushup(int rt){    if(s[rt].cov){        s[rt].sum = x[s[rt].r+1] - x[s[rt].l];        s[rt].segnum = 2;//竖边个数为2        s[rt].lseg = s[rt].rseg = true;    }    else if(s[rt].l == s[rt].r){//叶子结点        s[rt].sum = s[rt].segnum = 0;        s[rt].lseg = s[rt].rseg = false;    }    else{        s[rt].sum = s[lson].sum + s[rson].sum;        s[rt].segnum = s[lson].segnum + s[rson].segnum;        s[rt].lseg = s[lson].lseg;        s[rt].rseg = s[rson].rseg;        if(s[lson].rseg && s[rson].lseg) s[rt].segnum -= 2;//两个矩形相交(底边区域有重合)则减少两条竖边    }}void build(int l, int r, int rt){    s[rt].l = l;  s[rt].r = r;    s[rt].cov = s[rt].sum = s[rt].segnum = 0;    s[rt].lseg = s[rt].rseg = false;    if(l == r) return;    int mid = (l+r) >> 1;    build(l, mid, lson);    build(mid+1, r, rson);}void updata(int l, int r, int c, int rt){    if(l <= s[rt].l && s[rt].r <= r){        s[rt].cov += c;        pushup(rt);        return;    }    int mid = (s[rt].l + s[rt].r) >> 1;    if(l <= mid) updata(l, r, c, lson);    if(mid < r) updata(l, r, c, rson);    pushup(rt);}int main(){    int n,x1,x2,y1,y2,i,j;    while(~scanf("%d",&n))    {        int m = 0;        for(i = 0; i < n; i ++){            scanf("%d%d%d%d",&x1,&y1,&x2,&y2);            ss[m] = seg(x1, x2, y1, 1);            x[m++] = x1;            ss[m] = seg(x1, x2, y2, -1);            x[m++] = x2;        }        sort(x, x+m);        sort(ss, ss+m);        int k = 1;        for(i = 1; i < m; i ++)            if(x[i] != x[i-1]) x[k++] = x[i];        build(0, k, 1);        int ans = 0, front = 0;        for(i = 0; i < m; i ++){            int l = lower_bound(x, x+k, ss[i].l) - x;            int r = lower_bound(x, x+k, ss[i].r) - x - 1;            if(l <= r) updata(l, r, ss[i].c, 1);            ans += s[1].segnum*(ss[i+1].h - ss[i].h);//竖边增加的总长            ans += abs(s[1].sum - front);//底边增加的总长            front = s[1].sum;        }        printf("%d\n",ans);    }    return 0;}
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