Eight Queen Problem - Java Data Structure

Java examples for Data Structure:Algorithm

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Description

Eight Queen Problem

Demo Code

class Queen {/*w w  w. j  a  v  a 2  s  . c om*/
  static final int n = 8;
  static int[] queen = new int[n]; // position (i,queen[i])
  static int nbsol;

  static void displayChessboard() {
    int i, j;

    System.out.println("");

    for (i = 0; i < n; i++) {
      for (j = 0; j < n; j++) {
        if (queen[i] != j)
          System.out.print("0");
        else
          System.out.print("1");
      }
      System.out.println("");
    }
  }

  static boolean wrongPos(int i1, int j1, int i2, int j2) {
    return (i1 == i2 || j1 == j2 || Math.abs(i1 - i2) == Math.abs(j1 - j2));
  }

  // Place safely queen i at column j?
  static boolean safeMove(int i, int j) {
    boolean result = true;

    for (int k = 0; k < i; k++)
      result = result && !wrongPos(i, j, k, queen[k]);

    return result;
  }

  static boolean search(int row) {
    boolean result = false;

    if (row == n) {
      displayChessboard();
      nbsol++;
    } else {
      int j = 0;
      while (!result && j < n) {
        if (safeMove(row, j)) {
          queen[row] = j;
          result = search(row + 1);
        }
        // Backtracking here
        j++; // explore all columns
      }
    }
    return result;
  }

}

public class Main {
  public static void main(String[] arguments) {
    Queen.nbsol = 0;
    Queen.search(0);
    System.out.println("Total number of solutions:" + Queen.nbsol);
  }

}

Result


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