题意：

      给你n个矩形，问你这n个矩形所围成的图形的周长是多少。

思路：

      线段树的扫描线简单应用，这个题目我用的方法比较笨，就是扫描两次，上下扫描，求出多边形的上下边长和，然后同理左右扫描，求出多边形的左右边长的和，然后加起来就行了，还有这个题目有一个小小的提示，就是在重边的时候记得是先加边在删边。不然会多加边（这个地方不管也能AC显然是数据弱，不信的自己找一个简单的有重复边的测下就知道了）。

#include<stdio.h>

#include<string.h>

#include<algorithm>

#define lson l ,mid ,t << 1

#define rson mid ,r ,t << 1 | 1

#define N 50000


using namespace std;

typedef struct

{

   int l ,r ,h ,mk;

}EDGE;

typedef struct

{

   int x1 ,x2 ,y1 ,y2;

}NODE;

NODE node[5500];

EDGE edge[N];

int len[N] ,cnt[N];

int tmp[11000] ,num[11000];

bool camp(EDGE a ,EDGE b)

{

   return a.h < b.h || a.h == b.h && a.mk > b.mk;

}

int abss(int x)

{

   if(x < 0) return -x ;

   return x;

}

void Pushup(int l ,int r ,int t)

{

   if(cnt[t]) len[t] = num[r] - num[l];

   else if(l + 1 == r) len[t] = 0;

   else len[t] = len[t<<1] + len[t<<1|1];

}

void Update(int l ,int r ,int t ,int a ,int b ,int c)

{

   if(a == l && b == r)

   {

      cnt[t] += c;

      Pushup(l ,r ,t);

      return;

   }

   int mid = (l + r) >> 1;

   if(b <= mid) Update(lson ,a ,b ,c);

   else if(a >= mid) Update(rson ,a ,b ,c);

   else

   {

      Update(lson ,a ,mid ,c);

      Update(rson ,mid ,b ,c);

   }

   Pushup(l ,r ,t);

}

int search_2(int id ,int now)

{

   int low ,up ,mid ,ans;

   low = 1 ,up = id;

   while(low <= up)

   {

      mid = (low + up) >> 1;

      if(now <= num[mid])

      {

         ans = mid;

         up = mid - 1;

      }

      else low = mid + 1;

   }

   return ans;

}

int main ()

{

   int n ,i ,id ,sum;

   while(~scanf("%d" ,&n))

   {

      for(i = 1 ;i <= n ;i ++)

      scanf("%d %d %d %d" ,&node[i].x1 ,&node[i].y1 ,&node[i].x2 ,&node[i].y2);

      for(id = 0 ,i = 1 ;i <= n ;i ++)

      {

         edge[++id].l = node[i].x1;

         edge[id].r = node[i].x2 ,edge[id].h = node[i].y1 ,edge[id].mk = 1;

         tmp[id] = node[i].x1;

         edge[++id].l = node[i].x1;

         edge[id].r = node[i].x2 ,edge[id].h = node[i].y2 ,edge[id].mk = -1;

         tmp[id] = node[i].x2;

      }

      sort(tmp + 1 ,tmp + id + 1);

      sort(edge + 1 ,edge + id + 1 ,camp);

      for(id = 0 ,i = 1 ;i <= n * 2 ;i ++)

      if(i == 1 || tmp[i] != tmp[i-1]) num[++id] = tmp[i];

      sum = 0;

      memset(len ,0 ,sizeof(len));

      memset(cnt ,0 ,sizeof(cnt));

      int tt = 0;

      for(i = 1 ;i <= n * 2 ;i ++)

      {

         int l = search_2(id ,edge[i].l);

         int r = search_2(id ,edge[i].r);

         Update(1 ,id ,1 ,l ,r ,edge[i].mk);

         //printf("%d %d %d****\n" ,len[1] ,l ,r);

         sum += abs(len[1] - tt);

         tt = len[1];

      }

      //printf("%d\n" ,sum);
      for(id = 0 ,i = 1 ;i <= n ;i ++)

      {

         edge[++id].l = node[i].y1;

         edge[id].r = node[i].y2 ,edge[id].h = node[i].x1 ,edge[id].mk = 1;

         tmp[id] = node[i].y1;

         edge[++id].l = node[i].y1;

         edge[id].r = node[i].y2 ,edge[id].h = node[i].x2 ,edge[id].mk = -1;

         tmp[id] = node[i].y2;

      }

      sort(tmp + 1 ,tmp + id + 1);

      sort(edge + 1 ,edge + id + 1 ,camp);

      for(id = 0 ,i = 1 ;i <= n * 2 ;i ++)

      if(i == 1 || tmp[i] != tmp[i-1]) num[++id] = tmp[i];

      memset(len ,0 ,sizeof(len));

      memset(cnt ,0 ,sizeof(cnt));

      tt = 0;

      for(i = 1 ;i <= n * 2 ;i ++)

      {

         int l = search_2(id ,edge[i].l);

         int r = search_2(id ,edge[i].r);

         Update(1 ,id ,1 ,l ,r ,edge[i].mk);

         sum += abs(len[1] - tt);

         tt = len[1];

      }

      printf("%d\n" ,sum);

   }

   return 0;

}