Chapter 13, Problem 25PE

Program Plan Intro

N Queens Problem

Program plan:

Filename: “PartialSolution.java”

This code snippet creates a class “PartialSolution”. In the code,

• Define a class “PartialSolution”.
  • Declare the class variables.
  • Define the constructor “PartialSolution”.
    • Set “boardSize” equal to “n”.
    • Define the array “queens”.
  • Define the method “examine()”.
    • Iterate a “for” loop,
      • Iterate the inner “for” loop,
        • If “queens[i]” attacks “queens[j]”.
        • • Return the value of “ABANDON”.
            • If the length of the “queens” is “boardSize”,
              • Return the value of “ACCEPT”.
            • Else,
              • Return the value of “CONTINUE”.
  • Define the method “extend()”.
    • Set the value of “result”.
    • Iterate a “for” loop,
      • Get the length of “queens” to “size”.
      • Set the “result[i]”.
      • Iterate a “for” loop,
        • Set “queen[j]” to “result[i]”.
        • • • • • Append the new queen to “ith” column.
            • Return the value of “result”.
  • Define a method “toString()”.
    • Return the queens.

Filename: “Queen.java”

This code snippet creates a class “Queen”. In the code,

• Define a class “Queen”.
  • Define the class members “row” and “column”.
  • Define a constructor “Queen()”.
    • Set the value of “row” and “column”.
  • Define the method “attacks()”.
    • Return the result of logical operation.
  • Define a method “toString()”.
    • Return the value.

Filename: “NQueens.java”

This code snippet creates a class “NQueens”. In the code,

• Import the required packages.
• Define a class “NQueens”.
  • Define the “main” method.
    • Prompt the user to enter the number.
    • Define the object of class “Scanner”.
    • Scan for the input.
    • If the value of “n” is greater than or equal to 0,
      • Call the method “solve()”.
  • Define the method “solve()”.
    • Define the variable “exam”.
    • If the value of “exam” equal to “ACCEPT”,
      • Print the value of “sol”.
    • Else if, the value of “exam” is “ABANDON”,
      • Iterate a “for” loop,
        • Call the method “solve()”.