From 005d84d7807425594337401751728866b46a1d7a Mon Sep 17 00:00:00 2001
From: Graham Cox <graham@grahamcox.co.uk>
Date: Fri, 11 Aug 2023 11:57:48 +0100
Subject: [PATCH] BAEL-6813: Creating a Magic Square in Java (#14572)

---
 core-java-modules/core-java-leetcode/pom.xml  |  39 ++++
 .../magicsquare/GenerationUnitTest.java       |  45 +++++
 .../leetcode/magicsquare/MagicSquare.java     | 186 ++++++++++++++++++
 .../magicsquare/ValidationUnitTest.java       |  21 ++
 core-java-modules/pom.xml                     |   1 +
 5 files changed, 292 insertions(+)
 create mode 100644 core-java-modules/core-java-leetcode/pom.xml
 create mode 100644 core-java-modules/core-java-leetcode/src/test/java/com/baeldung/leetcode/magicsquare/GenerationUnitTest.java
 create mode 100644 core-java-modules/core-java-leetcode/src/test/java/com/baeldung/leetcode/magicsquare/MagicSquare.java
 create mode 100644 core-java-modules/core-java-leetcode/src/test/java/com/baeldung/leetcode/magicsquare/ValidationUnitTest.java

diff --git a/core-java-modules/core-java-leetcode/pom.xml b/core-java-modules/core-java-leetcode/pom.xml
new file mode 100644
index 0000000000..eb91308c64
--- /dev/null
+++ b/core-java-modules/core-java-leetcode/pom.xml
@@ -0,0 +1,39 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project xmlns="http://maven.apache.org/POM/4.0.0"
+    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+    xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+    <modelVersion>4.0.0</modelVersion>
+    <artifactId>core-java-leetcode</artifactId>
+    <name>core-java-leetcode</name>
+    <packaging>jar</packaging>
+
+    <parent>
+        <groupId>com.baeldung</groupId>
+        <artifactId>parent-modules</artifactId>
+        <version>1.0.0-SNAPSHOT</version>
+        <relativePath>../../pom.xml</relativePath>
+    </parent>
+
+    <dependencies>
+    </dependencies>
+
+    <build>
+        <plugins>
+            <plugin>
+                <groupId>org.apache.maven.plugins</groupId>
+                <artifactId>maven-compiler-plugin</artifactId>
+                <version>${maven-compiler-plugin.version}</version>
+                <configuration>
+                    <source>${maven.compiler.source.version}</source>
+                    <target>${maven.compiler.target.version}</target>
+                </configuration>
+            </plugin>
+        </plugins>
+    </build>
+
+    <properties>
+        <maven.compiler.source.version>11</maven.compiler.source.version>
+        <maven.compiler.target.version>11</maven.compiler.target.version>
+    </properties>
+
+</project>
diff --git a/core-java-modules/core-java-leetcode/src/test/java/com/baeldung/leetcode/magicsquare/GenerationUnitTest.java b/core-java-modules/core-java-leetcode/src/test/java/com/baeldung/leetcode/magicsquare/GenerationUnitTest.java
new file mode 100644
index 0000000000..308c655bd1
--- /dev/null
+++ b/core-java-modules/core-java-leetcode/src/test/java/com/baeldung/leetcode/magicsquare/GenerationUnitTest.java
@@ -0,0 +1,45 @@
+package com.baeldung.leetcode.magicsquare;
+
+import org.junit.jupiter.api.Test;
+
+public class GenerationUnitTest {
+    @Test
+    public void testGenerate3x3() {
+        MagicSquare magicSquare = new MagicSquare(3);
+        System.out.println(magicSquare);
+
+        magicSquare.validate();
+    }
+
+    @Test
+    public void testGenerate9x9() {
+        MagicSquare magicSquare = new MagicSquare(9);
+        System.out.println(magicSquare);
+
+        magicSquare.validate();
+    }
+
+    @Test
+    public void testGenerate12x12() {
+        MagicSquare magicSquare = new MagicSquare(12);
+        System.out.println(magicSquare);
+
+        magicSquare.validate();
+    }
+
+    @Test
+    public void testGenerate10x10() {
+        MagicSquare magicSquare = new MagicSquare(10);
+        System.out.println(magicSquare);
+
+        magicSquare.validate();
+    }
+
+    @Test
+    public void testGenerate18x18() {
+        MagicSquare magicSquare = new MagicSquare(18);
+        System.out.println(magicSquare);
+
+        magicSquare.validate();
+    }
+}
diff --git a/core-java-modules/core-java-leetcode/src/test/java/com/baeldung/leetcode/magicsquare/MagicSquare.java b/core-java-modules/core-java-leetcode/src/test/java/com/baeldung/leetcode/magicsquare/MagicSquare.java
new file mode 100644
index 0000000000..5e16f2e0db
--- /dev/null
+++ b/core-java-modules/core-java-leetcode/src/test/java/com/baeldung/leetcode/magicsquare/MagicSquare.java
@@ -0,0 +1,186 @@
+package com.baeldung.leetcode.magicsquare;
+
+import org.junit.platform.commons.util.StringUtils;
+
+import java.util.stream.IntStream;
+
+public class MagicSquare {
+    private int[][] cells;
+
+    public MagicSquare(int n) {
+        this.cells = new int[n][];
+
+        for (int i = 0; i < n; ++i) {
+            this.cells[i] = new int[n];
+        }
+
+        if (n % 2 == 1) {
+            populateOdd();
+        } else if (n % 4 == 0) {
+            populateDoubleEven();
+        } else if (n >= 6) {
+            populateSingleEven();
+        }
+    }
+
+    private void populateOdd() {
+        int n = getN();
+
+        populateOddArea(0, 0, n, 0);
+    }
+
+    private void populateOddArea(int xOffset, int yOffset, int n, int numberOffset) {
+        int y = 0;
+        int x = (n - 1) / 2;
+        setCell(xOffset + x, yOffset + y, numberOffset + 1);
+
+        for (int number = 2; number <= n * n; ++number) {
+            int nextX = x + 1;
+            if (nextX == n) {
+                nextX = 0;
+            }
+
+            int nextY = y - 1;
+            if (nextY == -1) {
+                nextY = n - 1;
+            }
+
+            if (getCell(xOffset + nextX, yOffset + nextY) != 0) {
+                nextX = x;
+
+                nextY = y + 1;
+                if (nextY == n) {
+                    nextY = 0;
+                }
+            }
+
+            setCell(xOffset + nextX, yOffset + nextY, numberOffset + number);
+
+            x = nextX;
+            y = nextY;
+        }
+    }
+
+    private void populateDoubleEven() {
+        int n = getN();
+        int number = 1;
+
+        for (int y = 0; y < n; ++y) {
+            for (int x = 0; x < n; ++x) {
+                boolean highlighted = false;
+
+                if ((y < n/4 || y >= 3*n/4) && (x >= n/4 && x < 3*n/4)) {
+                    highlighted = true;
+                } else if ((x < n/4 || x >= 3*n/4) && (y >= n/4 && y < 3*n/4)) {
+                    highlighted = true;
+                }
+
+                if (highlighted) {
+                    setCell(x, y, (n * n) - number + 1);
+                } else {
+                    setCell(x, y, number);
+                }
+
+                number += 1;
+            }
+        }
+    }
+
+    private void populateSingleEven() {
+        int n = getN();
+        int halfN = n/2;
+        int swapSize = (int) n/4;
+
+        populateOddArea(0, 0, halfN, 0);
+        populateOddArea(halfN, halfN, halfN, halfN * halfN);
+        populateOddArea(halfN, 0, halfN, (halfN * halfN) * 2);
+        populateOddArea(0, halfN, halfN, (halfN * halfN) * 3);
+
+        for (int x = 0; x < swapSize; ++x) {
+            swapCells(x, 0, x, halfN);
+            swapCells(x, halfN - 1, x, n - 1);
+
+            for (int y = 1; y < halfN - 1; ++y) {
+                swapCells(x + 1, y, x + 1, y + halfN);
+            }
+        }
+
+        for (int x = 0; x < swapSize - 1; ++x) {
+            for (int y = 0; y < halfN; ++y) {
+                swapCells(n - x - 1, y, n - x - 1, y + halfN);
+            }
+        }
+
+    }
+
+    private void swapCells(int x1, int y1, int x2, int y2) {
+        int cell1 = getCell(x1, y1);
+        int cell2 = getCell(x2, y2);
+
+        setCell(x1, y1, cell2);
+        setCell(x2, y2, cell1);
+    }
+
+    public int getN() {
+        return cells.length;
+    }
+
+    public int getCell(int x, int y) {
+        return cells[x][y];
+    }
+
+    public void setCell(int x, int y, int value) {
+        cells[x][y] = value;
+    }
+
+    public void validate() {
+        int n = getN();
+        int expectedValue = ((n * n * n) + n) / 2;
+
+        // Diagonals
+        if (IntStream.range(0, n).map(i -> getCell(i, i)).sum() != expectedValue) {
+            throw new IllegalStateException("Leading diagonal is not the expected value");
+        }
+        if (IntStream.range(0, n).map(i -> getCell(i, n - i - 1)).sum() != expectedValue) {
+            throw new IllegalStateException("Trailing diagonal is not the expected value");
+        }
+
+        // Rows
+        IntStream.range(0, n).forEach(y -> {
+            if (IntStream.range(0, n).map(x -> getCell(x, y)).sum() != expectedValue) {
+                throw new IllegalStateException("Row is not the expected value");
+            }
+        });
+
+        // Cols
+        IntStream.range(0, n).forEach(x -> {
+            if (IntStream.range(0, n).map(y -> getCell(x, y)).sum() != expectedValue) {
+                throw new IllegalStateException("Column is not the expected value");
+            }
+        });
+    }
+
+    public String toString() {
+        int n = getN();
+        int largestNumberLength = Integer.toString(n * n).length();
+        String formatString = " %0" + largestNumberLength + "d ";
+
+        StringBuilder sb = new StringBuilder();
+
+        for (int y = 0; y < n; ++y) {
+            for (int x = 0; x < n; ++x) {
+                int value = getCell(x, y);
+                if (value == 0) {
+                    sb.append(" ");
+                    sb.append(".".repeat(largestNumberLength));
+                    sb.append(" ");
+                } else {
+                    sb.append(String.format(formatString, value));
+                }
+            }
+            sb.append("\n");
+        }
+
+        return sb.toString();
+    }
+}
diff --git a/core-java-modules/core-java-leetcode/src/test/java/com/baeldung/leetcode/magicsquare/ValidationUnitTest.java b/core-java-modules/core-java-leetcode/src/test/java/com/baeldung/leetcode/magicsquare/ValidationUnitTest.java
new file mode 100644
index 0000000000..93f36931e6
--- /dev/null
+++ b/core-java-modules/core-java-leetcode/src/test/java/com/baeldung/leetcode/magicsquare/ValidationUnitTest.java
@@ -0,0 +1,21 @@
+package com.baeldung.leetcode.magicsquare;
+
+import org.junit.jupiter.api.Test;
+
+public class ValidationUnitTest {
+    @Test
+    public void testValidate3x3() {
+        MagicSquare magicSquare = new MagicSquare(3);
+        magicSquare.setCell(0, 0, 8);
+        magicSquare.setCell(1, 0, 1);
+        magicSquare.setCell(2, 0, 6);
+        magicSquare.setCell(0, 1, 3);
+        magicSquare.setCell(1, 1, 5);
+        magicSquare.setCell(2, 1, 7);
+        magicSquare.setCell(0, 2, 4);
+        magicSquare.setCell(1, 2, 9);
+        magicSquare.setCell(2, 2, 2);
+
+        magicSquare.validate();
+    }
+}
diff --git a/core-java-modules/pom.xml b/core-java-modules/pom.xml
index e9bb86e500..a6f0382186 100644
--- a/core-java-modules/pom.xml
+++ b/core-java-modules/pom.xml
@@ -108,6 +108,7 @@
         <module>core-java-lang-operators-2</module>
         <module>core-java-lang-syntax</module>
         <module>core-java-lang-syntax-2</module>
+        <module>core-java-leetcode</module>
         <module>core-java-locale</module>
         <module>core-java-networking</module>
         <module>core-java-networking-2</module>