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PO8 queens problem using backtracking recurison
 

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  1. PO8 queens problem using backtracking recurison
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    <p>I've been working on the 8 queens problem but I got stuck. I don't want code. I would love guidance and directions in order to understand how to solve this problem myself using backtracking recursion.</p> <p>The program should enumerate all solutions to the N-queens problem by drawing the location of the queens in ASCII like the two solutions <a href="http://img197.imageshack.us/img197/2595/8queens.jpg" rel="nofollow">here</a>. </p> <p>My pseudocode so far is: </p> <pre><code>void queen(int n){ for( int i = 0; i &lt; n; i++){ place queen[ i ] on row i; for(int j = 0 ; j &lt; n ; j++){ if( queen[ i ] is not in the same column as queen[0] through queen[ i - 1 ] &amp;&amp; queen[ i ] is not on the same major diagonal with queen[0] through queen[ i -1 ] &amp;&amp; queen[ i ] is not on the same minor diagonal with queen[0] through queen[ i -1 ] ) { print 'Q '; } else{ print '* '; } System.out.println(); } System.out.println(); } } </code></pre> <p>There is no any backtracking recursion in my pseudocode because I don't know how to do it.</p> <p>Any help is greatly appreciated.No code, please.</p> <p>(Update in response to Nemo):</p> <pre><code>solver(int n, Board b){ for(int i = 0; i &lt; b.length; i++){ place queen in column i; for(int j = 0; j &lt; b.length; j++){ change b; solver(n+1,changed b); } } } </code></pre> <p>Is it correct? </p> <p>(Update 2):</p> <pre><code> solver8(board /* with queens presented in first 7 columns */){ // place a queen in the 8th column; for(each possible placement of the queen in column 8 or in other words int i = 0; i &lt; board.length; i++ ){ place the queen and print the board } } solver7(board /* with queens presented in first 6 columns */){ // place a queen in the 7th column; for(each possible placement of the queen in column 7 or in other words int i = 0; i &lt; board.length; i++ ){ solver8(board with queens placed in first 7 columns); } } solver6(board /* with queens presented in first 5 columns */ ){ // place a queen in the 6th column; for(each possible placement of the queen in column 6 or in other words int i = 0; i &lt; board.length; i++ ){ solver7(board with queens presented in first 6 columns); } } </code></pre> <p>and so on until</p> <pre><code> solver1(1, empty board){ for(int i = 0; i &lt; board.length; i++){ place queen in row[i] of column 1; solver2(board with queen in row[i] of column 1); } } </code></pre> <p>Update 3 (Edited):</p> <pre><code>private int numberOfQueens = 8; solver(int n, Board b){ for(int r = 0; r &lt; b.length; r++){ place queen in row[r] of column[n]; if(n == numberOfQueens){ print the board; return; } else{ solver(n+1, board with queen in row[r] of column[n]); } } } } </code></pre>
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    1. COIs this homework? If so, you should tag the question as such. It might prevent people from giving you complete solutions that wouldn't help you at all.
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      1. USBertrand Marron
    2. CO+1 for explicitly requesting that we don't write the code for you. :-)
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      1. USAasmund Eldhuset
    3. CO@Bertrand: I wouldn't say it's homework since I am studying on my own.
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