Rokua P1141//bfs to find the sub-connected block size of undirected graphs (multiple queries)

http://www.luogu.org/problem/show?pid=1141

To ask questions, the size of the sub-connected block of undirected graphs is sought.

Direct BFS, read a search one, over 60;

100% points 1,000,000 points, 100,000 queries, is obviously memory.

I was weak, and I started out. The number group records the coordinates of the first point of each point belonging to the connected block, and then writes a bunch of them.

Later asked a great God, like the mist to see the sky. The "name" of the connected block is recorded with CNT.

Learned this trick, does not mean too.

I still read a point, if the output is accessed, the DFS is not accessed, and then each DFS is cycled once, assigning values to all the points within the connected block. The code is as follows

1#include <iostream>2#include <cstdio>3#include <cmath>4#include <string>5#include <cstring>6#include <queue>7#include <cstdlib>8#include <algorithm>9 #defineFor1 (i,n,m) for (int i= (n); i<= (m); i++)Ten #defineFor2 (i,n,m) for (int i= (n); i>= (m); i--) One using namespacestd; A intN,cnt=1, m,a[1005][1005],ans[1005][1005],v[1005][1005],f1[4]={0,0,1,-1},f2[4]={-1,1,0,0}; - structnode - { the     intx, y; - }; -Queue <node>Q; -  + voidBFsintXinty) - { +      A Q.push ({x, y}); atv[x][y]=CNT; -     intans1=0; -      while(!q.empty ()) -     {     -Node e=Q.front (); - Q.pop ();  inans1++; -For1 (I,0,3) to         { +             intx1=e.x+f1[i],y1=e.y+F2[i]; -             if(!v[x1][y1]&&a[x1][y1]==3-a[e.x][e.y]&&x1>0&&y1>0&&x1<=n&&y1<=N) the             { *              $v[x1][y1]=CNT;Panax Notoginseng Q.push ({x1,y1}); -             } the         } +     } AFor1 (I,1, N) theFor1 (J,1, N) +     { -         if(v[i][j]==CNT) $ans[i][j]=ans1; $              -     } -cnt++; the } - Wuyi intMain () the { -Cin>>n>>m; WuFor1 (I,1, N) -For1 (J,1, N) About     { $         CharCh=GetChar (); -          while(ch!='1'&&ch!='0') -Ch=GetChar (); -         if(ch=='1') Aa[i][j]=1; +         if(ch=='0') thea[i][j]=2; -     } $For1 (I,1, M) the     { the         intx, y; theCin>>x>>y; the         if(!V[x][y]) - BFS (x, y); incout<<ans[x][y]<<Endl;; the     } the}

Timeout Code

I'm so stupid, I didn't use CNT at all.

After the timeout, ask the great God.

He said the complexity should be O (n^2+m)

I'm a crazy face.

Take a closer look at his code and feel like he's got a bubble in his brain.

Then opened a t[I] array as a bucket, record the size of the Unicom block belonging to I.

Over DFS, ask for all connected blocks, and group them, respectively, to record the size.

Final output ...

The code is as follows

1#include <iostream>2#include <cstdio>3#include <cmath>4#include <string>5#include <cstring>6#include <queue>7#include <cstdlib>8#include <algorithm>9 #defineFor1 (i,n,m) for (int i= (n); i<= (m); i++)Ten #defineFor2 (i,n,m) for (int i= (n); i>= (m); i--) One using namespacestd; A intN,cnt=1, m,a[1005][1005],ans[1005][1005],f1[4]={0,0,1,-1},f2[4]={-1,1,0,0}; - intt[1005000];//use a bucket to record each group of ANS - intv[1005][1005];//grouping, assigning the same value to points within the same connected block, using CNT to count to denote the "first name" of the connected block the structnode - { -     intx, y; - }; +Queue <node>Q; -  + intBFsintXinty) A { at      - Q.push ({x, y}); -v[x][y]=CNT; -     intans1=0; -      while(!q.empty ()) -     {     inNode e=Q.front (); - Q.pop ();  toans1++; +For1 (I,0,3) -         { the             intx1=e.x+f1[i],y1=e.y+F2[i]; *             if(!v[x1][y1]&&a[x1][y1]==3-a[e.x][e.y]&&x1>0&&y1>0&&x1<=n&&y1<=N) $             {Panax Notoginseng              -v[x1][y1]=CNT; the Q.push ({x1,y1}); +             } A         } the     } +cnt++; -     returnans1; $ } $  - intMain () - { theCin>>n>>m; -For1 (I,1, N)WuyiFor1 (J,1, N) the     { -         CharCh=GetChar (); Wu          while(ch!='1'&&ch!='0') -Ch=GetChar (); About         if(ch=='1') $a[i][j]=1; -         if(ch=='0') -a[i][j]=2; -     } AFor1 (I,1, N) +For1 (J,1, N) the         { -             if(!V[i][j]) $             { the                 inttmp=BFS (i,j); thet[cnt-1]=tmp; the         }} theFor1 (I,1, M) -     { in         intx, y; theCin>>x>>y; the          Aboutcout<<t[v[x][y]]<<Endl; the     } the}

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Rokua P1141//bfs to find the sub-connected block size of undirected graphs (multiple queries)