4N 魔方陣

簡單的說，就是一個從左上由1依序開始填，但遇對角線不填，另一個由左上由16開始填，但只填在對角線，再將兩個合起來就是解答了；如果N大於2，則以 4X4為單位畫對角線：

至於對角線的位置該如何判斷，有兩個公式，有興趣的可以畫圖印證看看，如下所示：

實作：C    Java    Python    Scala    Ruby

• C

#include <stdio.h> 
#include <stdlib.h> 

#define N 8 

int main(void) { 
    int square[N+1][N+1] = {0}; 

    int i, j; 
    for(j = 1; j <= N; j++) { 
        for(i = 1; i <= N; i++){ 
            if(j % 4 == i % 4 || (j % 4 + i) % 4 == 1) 
                square[i][j] = (N+1-i) * N -j + 1; 
            else 
                square[i][j] = (i - 1) * N + j; 
        } 
    } 

    for(i = 1; i <= N; i++) { 
        for(j = 1; j <= N; j++) 
            printf("%2d ", square[i][j]); 
        printf("\n"); 
    } 

    return 0; 
} 

• Java

public class Matrix {
    public static int[][] magic(int n) {
        int[][] square = new int[n+1][n+1]; 

        for(int j = 1; j <= n; j++) { 
            for(int i = 1; i <= n; i++){ 
                if(j % 4 == i % 4 || (j % 4 + i) % 4 == 1) 
                    square[i][j] = (n+1-i) * n -j + 1; 
                else 
                    square[i][j] = (i - 1) * n + j; 
            } 
        } 
        
        int[][] matrix = new int[n][n];
        
        for(int k = 0; k < matrix.length; k++) {
           for(int l = 0; l < matrix[0].length; l++) {
               matrix[k][l] = square[k+1][l+1];
           }
        }
        
        return matrix;
    }
   
    public static void main(String[] args) {
        for(int[] row : Matrix.magic(8)) {
            for(int number: row) {
                System.out.printf("%2d ", number);
            }
            System.out.println();
         }
    }
}

• Python

def magic(n):
    square = []
    for i in range(n + 1):
        square.append([0] * (n + 1))
    for j in range(1, n + 1):
        for i in range(1, n + 1):
            if j % 4 == i % 4 or (j % 4 + i) % 4 == 1:
                square[i][j] = (n + 1 - i) * n - j + 1
            else:
                square[i][j] = (i - 1) * n + j
    matrix = []
    for i in range(n):
        matrix.append([0] * n)
    for k in range(len(matrix)):
        for l in range(len(matrix[0])):
            matrix[k][l] = square[k + 1][l + 1]
    return matrix

matrix = magic(8)
print(matrix)

• Scala

object Matrix {
    def magic(n: Int) = {
        val square = new Array[Array[Int]](n + 1, n + 1)

        for(j <- 1 to n; i <- 1 to n) {
            square(i)(j) = if(j % 4 == i % 4 || (j % 4 + i) % 4 == 1)
                               (n+1-i) * n -j + 1
                           else 
                               (i - 1) * n + j
        }
        
        val matrix = new Array[Array[Int]](n, n)
        for(k <- 0 until matrix.length; l <- 0 until matrix(0).length) {
            matrix(k)(l) = square(k + 1)(l + 1)
        }
        matrix
    }
}

Matrix.magic(8).foreach(row => {
    row.foreach(number => printf("%2d ", number))
    println()
})

• Ruby

def magic(n)
    square = Array.new(n + 1) {
        Array.new(n + 1, 0)
    }
    1.upto(n) { |j|
        1.upto(n) { |i|
            if j % 4 == i % 4 || (j % 4 + i) % 4 == 1
                square[i][j] = (n + 1 - i) * n - j + 1
            else
                square[i][j] = (i - 1) * n + j
            end
        }
    }
    matrix = Array.new(n) {
        Array.new(n, 0)
    }
    matrix.length.times { |k|
        matrix[0].length.times { |l|
            matrix[k][l] = square[k + 1][l + 1]
        }
    }
    
    matrix
end

matrix = magic(8)
p matrix