UVA11882 biggest number (dfs+ pruning)

Links: http://vjudge.net/problem/23314

Analysis: Two kinds of pruning schemes.

1. Find out the number of points that can be reached at the current location (although the number of points actually can be reached is smaller than it, but optimistic estimates can be), if the current number plus the number is still less than the current optimal solution length, then pruning.

2. If the number can be reached from small to Dalian after the current number, if still less than the current optimal solution, then pruning. (Find out all the points that can still be reached with the BFS implementation (optimistic estimate)).

1#include <cstdio>2#include <algorithm>3#include <cstring>4#include <iostream>5#include <cstring>6#include <queue>7 using namespacestd;8 9 Const intMAXN = the+5;Ten  One intN, M, v[ -]; A stringans; - CharMAZE[MAXN][MAXN]; - BOOLVIS[MAXN][MAXN], MARK[MAXN][MAXN]; the  - BOOLSmallerstringnum) { -     if(Num.size () > Ans.size ())return true; -     Else if(num.size () = = Ans.size () && num > Ans)return true; +     Else return false; - } +  A Const intdx[4] = {1, -1,0,0}; at Const intdy[4] = {0,0,1, -1}; - intBFsintXinty) { -queue<pair<int,int> >Q; -memset (Mark,0,sizeof(Mark)); - Q.push (Make_pair (x, y)); -Mark[x][y] =true; in     intCNT =0; -      while(!Q.empty ()) { topair<int,int> U =Q.front (); Q.pop (); +          for(intDIR =0; Dir <4; dir++) { -             intNX = U.first + Dx[dir], NY = U.second +Dy[dir]; the             if(NX <1|| NX > N | | NY <1|| NY > M)Continue; *             if(Maze[nx][ny] = ='#'|| Vis[nx][ny] | | Mark[nx][ny])Continue; $Mark[nx][ny] =true;Panax Notoginsengv[cnt++] = Maze[nx][ny]-'0'; - Q.push (Make_pair (NX, NY)); the         } +     } A     returnCNT; the } +  - voidDfsintXintYstringnum) { $     if(smaller (num)) ans =num; $     Else { -         intCNT =BFS (x, y); -         if(Num.size () + CNT < ans.size ())return; the         if(Num.size () + cnt = =ans.size ()) { -Sort (V, v +CNT);Wuyi             stringnum2 =num; the              for(inti = cnt-1; I >=0; i--) -Num2 + =Char(V[i] +'0'); Wu             if(!smaller (NUM2))return; -         } About     } $      for(intDIR =0; Dir <4; dir++) { -         intNX = x + Dx[dir], NY = y +Dy[dir]; -         if(NX <1|| NX > N | | NY <1|| NY > M)Continue; -         if(Maze[nx][ny] = ='#')Continue; A         if(Vis[nx][ny])Continue;ElseVis[nx][ny] =true; +DFS (NX, NY, NUM +Maze[nx][ny]); theVis[nx][ny] =false; -     } $ } the  thevoidsolve () { the      for(inti =1; I <= N; i++) the          for(intj =1; J <= M; J + +) { -             if(Maze[i][j] = ='#')Continue; inmemset (Vis,false,sizeof(Vis)); theVIS[I][J] =true; the             stringnum =""; Aboutnum + =Maze[i][j]; the Dfs (i, J, num); the         } thecout << ans <<Endl; + } -  the intMain () {Bayi      while(Cin >> n >> M &&N) { the          for(inti =1; I <= N; i++) scanf ("%s", Maze[i] +1); the ans.clear (); solve (); -     } -     return 0; the}

UVA11882 biggest number (dfs+ pruning)