matrices

build.gradle.kts

@@ -5,7 +5,7 @@ plugins {
 }
 
 group = "me.alex_s168"
-version = "0.10"
+version = "0.11"
 
 repositories {
     mavenCentral()

src/main/kotlin/blitz/collections/FindCommon.kt

@@ -0,0 +1,15 @@
+package blitz.collections
+
+/** Returns the element that is at all positions in the list (if there is one) */
+fun <T> Iterable<T>.findCommon(): T? =
+    firstOrNull()?.let { first ->
+        if (all { it == first }) first
+        else null
+    }
+
+/** Returns the element that is at all positions in the list (if there is one) */
+fun <T> Sequence<T>.findCommon(): T? =
+    firstOrNull()?.let { first ->
+        if (all { it == first }) first
+        else null
+    }

src/main/kotlin/blitz/collections/Matrix.kt

@@ -0,0 +1,70 @@
+package blitz.collections
+
+import kotlin.math.min
+
+class Matrix<T>(
+    val width: Int,
+    val height: Int,
+    private val init: (x: Int, y: Int) -> T
+) {
+    val rows = MutableList(height) { y ->
+        MutableList(width) { x ->
+            init(x, y)
+        }
+    }
+
+    operator fun get(x: Int, y: Int): T =
+        rows[y][x]
+
+    operator fun set(x: Int, y: Int, value: T) {
+        rows[y][x] = value
+    }
+
+    fun transposeCopy(): Matrix<T> =
+        Matrix(width, height) { x, y -> this[y, x] }
+
+    fun perfectSquareCopy(): Matrix<T> =
+        min(width, height).let { wh ->
+            Matrix(wh, wh) { x, y -> this[x, y] }
+        }
+
+    fun copy(): Matrix<T> =
+        Matrix(width, height) { x, y -> this[x, y] }
+
+    fun diagonalTopLeftToBottomRight(to: MutableList<T> = mutableListOf()): MutableList<T> {
+        repeat(min(width, height)) { pos ->
+            to.add(this[pos, pos])
+        }
+        return to
+    }
+
+    fun diagonalTopRightToBottomLeft(to: MutableList<T> = mutableListOf()): MutableList<T> {
+        val wh = min(width, height)
+        for(pos in wh - 1 downTo 0) {
+            to.add(this[pos, wh - 1 - pos])
+        }
+        return to
+    }
+
+    fun diagonals(to: MutableList<MutableList<T>> = mutableListOf()): MutableList<MutableList<T>> {
+        to.add(diagonalTopLeftToBottomRight())
+        to.add(diagonalTopRightToBottomLeft())
+        return to
+    }
+
+    // TODO: make better
+    override fun toString(): String =
+        "--\n" +
+        rows.joinToString(separator = "\n") {
+            it.joinToString(separator = ", ", prefix = "| ", postfix = " |")
+        } + "\n--"
+}
+
+fun main() {
+    val mat = Matrix(3, 3) { x, y -> x * (3-y) }
+    println(mat)
+
+    println(mat.transposeCopy())
+
+    println(mat.diagonals())
+}