From 557616dc12ba71ae35f17bbb3fc685d7b2937cee Mon Sep 17 00:00:00 2001
From: Krisna Pranav <68631244+krishpranav@users.noreply.github.com>
Date: Mon, 7 Apr 2025 20:28:29 +0530
Subject: [PATCH] [ADD]: Generic Matrix<T> 2D Array Type to Kotlin Standard
 Library

---
 .../stdlib/src/kotlin/collections/Matrix.kt   | 124 ++++++++++++++++++
 1 file changed, 124 insertions(+)
 create mode 100644 libraries/stdlib/src/kotlin/collections/Matrix.kt

diff --git a/libraries/stdlib/src/kotlin/collections/Matrix.kt b/libraries/stdlib/src/kotlin/collections/Matrix.kt
new file mode 100644
index 0000000000000..83d212c1dea51
--- /dev/null
+++ b/libraries/stdlib/src/kotlin/collections/Matrix.kt
@@ -0,0 +1,124 @@
+/*
+ * Copyright 2010-2020 JetBrains s.r.o. and Kotlin Programming Language contributors.
+ * Use of this source code is governed by the Apache 2.0 license that can be found in the license/LICENSE.txt file.
+ */
+
+package kotlin.collections
+
+import kotlin.js.JsName
+
+/**
+ * A generic 2D matrix backed by a 1D array for memory efficiency.
+ *
+ * The matrix provides O(1) access to elements by row and column indices.
+ *
+ * @param T the type of elements contained in the matrix.
+ * @property rows number of rows in the matrix.
+ * @property columns number of columns in the matrix.
+ * @constructor Creates a new matrix with the specified [rows] and [columns], initialized by the [init] function.
+ */
+@SinceKotlin("1.9")
+public class Matrix<T> private constructor(
+    public val rows: Int,
+    public val columns: Int,
+    private val data: Array<Any?>
+) {
+    /**
+     * Creates a new matrix with the specified [rows] and [columns], initialized by the [init] function.
+     *
+     * @throws IllegalArgumentException if [rows] or [columns] are negative.
+     */
+    public constructor(
+        rows: Int,
+        columns: Int,
+        init: (Int, Int) -> T
+    ) : this(
+        rows,
+        columns,
+        Array(rows * columns) { i -> init(i / columns, i % columns) }
+    ) {
+        require(rows >= 0) { "Rows must be non-negative: $rows" }
+        require(columns >= 0) { "Columns must be non-negative: $columns" }
+    }
+
+    /**
+     * Returns the element at the specified [row] and [column] in the matrix.
+     *
+     * @throws IndexOutOfBoundsException if [row] or [column] is out of bounds.
+     */
+    @Suppress("UNCHECKED_CAST")
+    public operator fun get(row: Int, column: Int): T {
+        checkIndices(row, column)
+        return data[index(row, column)] as T
+    }
+
+    /**
+     * Sets the element at the specified [row] and [column] in the matrix to the given [value].
+     *
+     * @throws IndexOutOfBoundsException if [row] or [column] is out of bounds.
+     */
+    public operator fun set(row: Int, column: Int, value: T) {
+        checkIndices(row, column)
+        data[index(row, column)] = value
+    }
+
+    private fun index(row: Int, column: Int): Int = row * columns + column
+
+    private fun checkIndices(row: Int, column: Int) {
+        if (row !in 0 until rows) throw IndexOutOfBoundsException("Row index out of range: $row")
+        if (column !in 0 until columns) throw IndexOutOfBoundsException("Column index out of range: $column")
+    }
+
+    /**
+     * Returns a string representation of the matrix.
+     */
+    override fun toString(): String = buildString {
+        for (r in 0 until rows) {
+            for (c in 0 until columns) {
+                append(get(r, c)).append('\t')
+            }
+            appendLine()
+        }
+    }
+
+    override fun equals(other: Any?): Boolean {
+        if (this === other) return true
+        if (other !is Matrix<*>) return false
+        if (rows != other.rows || columns != other.columns) return false
+
+        for (r in 0 until rows) {
+            for (c in 0 until columns) {
+                if (get(r, c) != other.get(r, c)) return false
+            }
+        }
+        return true
+    }
+
+    override fun hashCode(): Int {
+        var result = rows
+        result = 31 * result + columns
+        for (element in data) {
+            result = 31 * result + (element?.hashCode() ?: 0)
+        }
+        return result
+    }
+
+    /**
+     * Returns new array of type `Array<Any?>` with the elements of this matrix.
+     */
+    @JsName("toArray")
+    protected open fun toArray(): Array<Any?> = data.copyOf()
+
+    /**
+     * Creates an iterator over the elements of the matrix in row-major order.
+     */
+    public operator fun iterator(): Iterator<T> = object : Iterator<T> {
+        private var index = 0
+        override fun hasNext(): Boolean = index < data.size
+        override fun next(): T {
+            if (!hasNext()) throw NoSuchElementException()
+            @Suppress("UNCHECKED_CAST")
+            return data[index++] as T
+        }
+    }
+}
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