POJ1177+线段树+扫描线

思路：

以y的值进行离散化

根据x的值 对每一条y轴边进行处理，如果是"左边"则插入，是"右边"则删除。

/*扫描线+线段树+离散化求多个矩形的周长*/#include<stdio.h>#include<string.h>#include<stdlib.h>#include<algorithm>#include<iostream>#include<queue>#include<stack>#include<math.h>#include<map>using namespace std;const int maxn = 5005;const int maxm = 10010;struct SegTree{int l,r;int len;//区间代表的长度int segnum;//区间被分成的段数int cover;//区间被覆盖的次数int sum;//区间被覆盖的总长度bool lcover,rcover;}ST[ maxm<<2 ];struct Line{int st,ed,x;//竖边的两个y值bool InOut;//是否为左边bool operator < (Line L) const{return x<L.x;}};Line yLine[ maxm ];int yIndex[ maxm ];int n;void build( int L,int R,int n ){ST[ n ].l = L;ST[ n ].r = R;ST[ n ].len = yIndex[ R ]-yIndex[ L ];ST[ n ].sum = ST[ n ].cover = ST[ n ].segnum = 0;ST[ n ].lcover = ST[ n ].rcover = false;if( R-L>1 ){int mid = (L+R)/2;build( L,mid,2*n );build( mid,R,2*n+1 );}return ;}void Update_Len( int n ){if( ST[n].cover>0 ){ST[n].sum = ST[n].len;}else if( ST[n].r-ST[n].l>1 ){ST[n].sum = ST[2*n].sum+ST[2*n+1].sum;}elseST[n].sum = 0;}void Update_Segnum( int n ){if( ST[n].cover>0 ){ST[n].lcover = ST[n].rcover = true;ST[n].segnum = 1;}else if( ST[n].r-ST[n].l>1 ){ST[n].lcover = ST[2*n].lcover;ST[n].rcover = ST[2*n+1].rcover;ST[n].segnum = ST[2*n].segnum+ST[2*n+1].segnum-ST[2*n].rcover*ST[2*n+1].lcover;}else{ST[n].segnum = 0;ST[n].lcover = ST[n].rcover = false;}}void PushUp ( int n ){Update_Len( n );Update_Segnum( n );}void Insert( int left,int right,int n ){if( ST[ n ].l==left&&ST[ n ].r==right ){ST[ n ].cover++;}else {int mid = (ST[ n ].l+ST[ n ].r)/2;if( right<=mid )Insert( left,right,2*n );else if( left>=mid )Insert( left,right,2*n+1 );else{Insert( left,mid,2*n );Insert( mid,right,2*n+1 );}}PushUp( n );}void Delete( int left,int right,int n ){if( ST[ n ].l==left&&ST[ n ].r==right ){ST[ n ].cover--;}else {int mid = (ST[ n ].l+ST[ n ].r)/2;if( right<=mid )Delete( left,right,2*n );else if( left>=mid )Delete( left,right,2*n+1 );else{Delete( left,mid,2*n );Delete( mid,right,2*n+1 );}}PushUp( n );}int GetIndex( int value ,int cnt ){return lower_bound(yIndex,yIndex+cnt,value )-yIndex;}int main(){while( scanf("%d",&n)==1 ){int cnt = 0;int x1,y1,x2,y2;for( int i=0;i<n;i++ ){scanf("%d%d%d%d",&x1,&y1,&x2,&y2);yLine[ 2*i ].x = x1;yLine[ 2*i+1 ].x = x2;yLine[ 2*i ].st = yLine[ 2*i+1 ].st = y1; yLine[ 2*i ].ed = yLine[ 2*i+1 ].ed = y2;yLine[ 2*i ].InOut = true;yLine[ 2*i+1 ].InOut = false;yIndex[ 2*i ] = y1;yIndex[ 2*i+1 ] = y2;}sort( yIndex,yIndex+2*n );sort( yLine,yLine+2*n );for( int i=1;i<2*n;i++ ){if( yIndex[i]!=yIndex[i-1] )yIndex[cnt++] = yIndex[i-1];}yIndex[cnt++] = yIndex[2*n-1];build( 0,cnt-1,1 );int Ans = 0;int PreSum = 0;;for( int i=0;i<2*n-1;i++ ){if( yLine[i].InOut ){Insert( GetIndex(yLine[i].st,cnt),GetIndex(yLine[i].ed,cnt),1 );}else{Delete( GetIndex(yLine[i].st,cnt),GetIndex(yLine[i].ed,cnt),1 );}Ans += ST[1].segnum*2*(yLine[i+1].x-yLine[i].x);Ans += abs(ST[1].sum-PreSum);PreSum = ST[1].sum;}Delete( GetIndex(yLine[2*n-1].st,cnt),GetIndex(yLine[2*n-1].ed,cnt),1 );Ans += abs(ST[1].sum-PreSum);printf("%d\n",Ans);}return 0;}