Depth first search Code[vs] 1295 n Queen's question

/*dfs, the key: Check the status of the Queen will attack. Two methods: (Second, faster) (1) void Solve (int row, int colused);   General approach, the method of judging whether the state is illegal: column through the bitwise operation; left oblique, right oblique through traversal. 

(2) void solvebitoperation (unsigned col, unsigned tiltleft, unsigned tiltright), full-bit operation, specific reference code comment. Also can refer to Matrix67 's blog (with image, very image):http://www.matrix67.com/blog/archives/266C + + implementation reference:http://www.cnblogs.com /lee41sum/archive/2010/04/22/1717986.html* *

1#include <iostream>2#include <cstdlib>3#include <cstdio>4#include <cstddef>5#include <iterator>6#include <algorithm>7#include <string>8#include <locale>9#include <cmath>Ten#include <vector> One#include <cstring> A#include <map> -#include <utility> -#include <queue> the#include <stack> -#include <Set> - using namespacestd; - Const intINF =-0x3f3f3f3f; + Const intMAXN = -; - Const intModprime =3046721; +  A intN; at BOOLisusednode[ -][ -]; - intAnswer =0; -  - //----------------------------------method One---------------------------------- - BOOLIsattack (intRowintColintcolused) - { in     if(colused& (1<<col)) -     { to         return true; +     } -      for(inti = row-1, j = col-1, k = col +1; i >0; -------j, + +k) the     { *         if(J >0) $         {Panax Notoginseng             if(Isusednode[i][j]) -             { the                 return true; +             } A         } the         if(k <=N) +         { -             if(Isusednode[i][k]) $             { $                 return true; -             } -         } the     } -     return false;Wuyi } the  - voidSolve (intRowintcolused) Wu { -     if(Row = = n+1) About     { $++answer; -         return; -     } -      for(intCol =1; Col <= N; ++Col) A     { +         if(!isattack (Row, col, colused)) the         { -Isusednode[row][col] =true; $Solve (Row +1, colused | (1<<col)); theIsusednode[row][col] =false; the         } the     } the } -  in //----------------------------------method and---------------------------------- theunsigned limN;//N Queens Target State (all columns already have queens, note: Columns here are compressed n rows into a row, with N columns in total) the voidsolvebitoperation (unsigned col, unsigned tiltleft, unsigned tiltright) About{//The illegal position of an illegal position created by a left oblique. the     if(col = =LimN) the     { the         //all columns already have Queens +++answer; -         return; the     }Bayiunsigned freeposset = limn& (~ (Col | tiltleft | tiltright));//get a collection of columns that do not conflict the      while(Freeposset) the     { -unsigned freepos = freeposset& ((~freeposset) +1);  -         //in the column collection that does not conflict, get the rightmost column position (if you can't think of the reason for the statement, take an example and deduce it yourself) the         /* the eg: the freeposset binary: 01010010 the ~freeposset binary: 10101101 - (~freeposset) +1 binary: 10101110 the freeposset& ((~freeposset) + 1) binary: 00000010 the  the         */94Freeposset-=Freepos; the         //In a column collection without conflicts, remove the position of the column where the current row has been used theSolvebitoperation (Col | freepos, (tiltleft | freepos) <<1, (Tiltright | freepos) >>1); the             //to the next line: Add an illegal column position (that is, the column position of the current row queen)98             //because the current line more than a queen, so left oblique to the next line more an illegal position, right oblique to the next line more than an illegal position About     } - }101 102 intMain ()103 {104 #ifdef HOME theFreopen ("inch","R", stdin);106     //freopen ("Out", "w", stdout);107 #endif108 109memset (Isusednode,false,sizeof(Isusednode)); theCIN >>N;111     //Method One the     //Solve (1, 0);113     //Method Two theLimN = (1<< N)-1; theSolvebitoperation (0,0,0); thecout << Answer <<Endl;117 118 #ifdef HOME119Cerr <<"Time Elapsed:"<< clock ()/Clocks_per_sec <<"Ms"<<Endl; - _CrtDumpMemoryLeaks ();121 #endif122     return 0;123}

Depth-First search Code[vs] 1295 n Queen question