Data commit

Task/Straddling-checkerboard/Kotlin/straddling-checkerboard.kotlin

@@ -0,0 +1,81 @@
+// version 1.2.0
+
+val board = "ET AON RISBCDFGHJKLMPQ/UVWXYZ."
+val digits = "0123456789"
+val rows = " 26"
+val escape = "62"
+val key = "0452"
+
+fun encrypt(message: String): String {
+    val msg = message.toUpperCase()
+                     .filter { (it in board || it in digits) && it !in " /" }
+    val sb = StringBuilder()
+    for (c in msg) {
+        val idx = board.indexOf(c)
+        if (idx > -1) {
+            val row = idx / 10
+            val col = idx % 10
+            sb.append(if (row == 0) "$col" else "${rows[row]}$col")
+        }
+        else {
+            sb.append("$escape$c")
+        }
+    }
+    val enc = sb.toString().toCharArray()
+    for ((i, c) in enc.withIndex()) {
+        val k = key[i % 4] - '0'
+        if (k == 0) continue
+        val j = c - '0'
+        enc[i] = '0' + ((j + k) % 10)
+    }
+    return String(enc)
+}
+
+fun decrypt(encoded: String): String {
+    val enc = encoded.toCharArray()
+    for ((i, c) in enc.withIndex()) {
+        val k = key[i % 4] - '0'
+        if (k == 0) continue
+        val j = c - '0'
+        enc[i] = '0' + if (j >= k) (j - k) % 10 else (10 + j - k) % 10
+    }
+    val len = enc.size
+    val sb = StringBuilder()
+    var i = 0
+    while (i < len) {
+        val c = enc[i]
+        val idx = rows.indexOf(c)
+        if (idx == -1) {
+            val idx2 = c - '0'
+            sb.append(board[idx2])
+            i++
+        }
+        else if ("$c${enc[i + 1]}" == escape) {
+            sb.append(enc[i + 2])
+            i += 3
+        }
+        else {
+            val idx2 = idx * 10 + (enc[i + 1] - '0')
+            sb.append(board[idx2])
+            i += 2
+        }
+    }
+    return sb.toString()
+}
+
+fun main(args: Array<String>) {
+    val messages = listOf(
+        "Attack at dawn",
+        "One night-it was on the twentieth of March, 1888-I was returning",
+        "In the winter 1965/we were hungry/just barely alive",
+        "you have put on 7.5 pounds since I saw you.",
+        "The checkerboard cake recipe specifies 3 large eggs and 2.25 cups of flour."
+    )
+    for (message in messages) {
+        val encrypted = encrypt(message)
+        val decrypted = decrypt(encrypted)
+        println("\nMessage   : $message")
+        println("Encrypted : $encrypted")
+        println("Decrypted : $decrypted")
+    }
+}