题目：http://poj.org/problem?id=1389题意：给出n个矩形的左下角和右上角，求出所有矩形面积的并思路：线段树+离散化+扫描线#include <stdio.h>#include <algorithm>#include <iostream>using namespace std;const int maxn=2000;struct SegMentTree{int l, r, cover, len, sum;}st[maxn<<2];struct Line{int y_top, y_btm, x;int in;bool operator<(Line l) const {return x<l.x;}}l[maxn+10];int y[maxn+10], ans, cnt;void BuildTree(int v, int left, int right){st[v].l=left, st[v].r=right, st[v].cover=0, st[v].len=y[right]-y[left];if (right-left==1){st[v].sum=0;return;}int lc=v<<1;int rc=lc+1;int mid=(left+right)>>1;BuildTree(lc, left, mid);BuildTree(rc, mid, right);st[v].sum=st[lc].sum+st[rc].sum;}void Update(int x){if (st[x].cover>0) st[x].sum=st[x].len;else if (st[x].r-st[x].l>1) st[x].sum=st[x*2].sum+st[x*2+1].sum;else st[x].sum=0;}void Insert(int v, int left, int right){if (st[v].l==left&&st[v].r==right) st[v].cover++;else{int lc=v<<1;int rc=lc+1;int mid=(st[v].l+st[v].r)>>1;if (right<=mid) Insert(lc, left, right);else if (left>=mid) Insert(rc, left, right);else {Insert(lc, left, mid);Insert(rc, mid, right);} }Update(v);}void Delete(int v, int left, int right){if (st[v].l==left&&st[v].r==right) st[v].cover--;else{int lc=v<<1;int rc=lc+1;int mid=(st[v].l+st[v].r)>>1;if (right<=mid) Delete(lc, left, right);else if (left>=mid) Delete(rc, left, right);else{Delete(lc, left, mid);Delete(rc, mid, right);}}Update(v);}int GetIndex(int x){return lower_bound(y, y+cnt, x)-y;}int main(){//freopen("in.txt", "r", stdin);int x1, y1, x2, y2;while (scanf("%d %d %d %d", &x1, &y1, &x2, &y2)==4){int i=0;if (x1==-1&&y1==-1&&x2==-1&&y2==-1) break;do{l[i*2].y_top=l[i*2+1].y_top=y1; l[i*2].y_btm=l[i*2+1].y_btm=y2;l[i*2].x=x1, l[i*2+1].x=x2;l[i*2].in=1, l[i*2+1].in=0;y[i*2]=y1, y[i*2+1]=y2;i++;}while (scanf("%d %d %d %d", &x1, &y1, &x2, &y2)&&(x1!=-1&&y1!=-1&&x2!=-1&&y2!=-1));sort(y, y+2*i);sort(l, l+2*i);cnt=0;for (int j=1; j<2*i; j++){if (y[j]!=y[j-1]) y[cnt++]=y[j-1];}y[cnt++]=y[2*i-1];BuildTree(1, 0, cnt-1);ans=0;for (int j=0; j<2*i-1; j++){if (l[j].in) Insert(1, GetIndex(l[j].y_top), GetIndex(l[j].y_btm));else Delete(1, GetIndex(l[j].y_top), GetIndex(l[j].y_btm));ans+=(l[j+1].x-l[j].x)*st[1].sum;}printf("%d\n", ans);}}
