June 2018 Update

Task/Arithmetic-evaluation/Kotlin/arithmetic-evaluation.kotlin

@@ -0,0 +1,86 @@
+// version 1.2.10
+
+/* if string is empty, returns zero */
+fun String.toDoubleOrZero() = this.toDoubleOrNull() ?: 0.0
+
+fun multiply(s: String): String {
+    val b = s.split('*').map { it.toDoubleOrZero() }
+    return (b[0] * b[1]).toString()
+}
+
+fun divide(s: String): String {
+    val b = s.split('/').map { it.toDoubleOrZero() }
+    return (b[0] / b[1]).toString()
+}
+
+fun add(s: String): String {
+    var t = s.replace(Regex("""^\+"""), "").replace(Regex("""\++"""), "+")
+    val b = t.split('+').map { it.toDoubleOrZero() }
+    return (b[0] + b[1]).toString()
+}
+
+fun subtract(s: String): String {
+    var t = s.replace(Regex("""(\+-|-\+)"""), "-")
+    if ("--" in t) return add(t.replace("--", "+"))
+    val b = t.split('-').map { it.toDoubleOrZero() }
+    return (if (b.size == 3) -b[1] - b[2] else b[0] - b[1]).toString()
+}
+
+fun evalExp(s: String): String {
+    var t = s.replace(Regex("""[()]"""), "")
+    val reMD = Regex("""\d+\.?\d*\s*[*/]\s*[+-]?\d+\.?\d*""")
+    val reM  = Regex( """\*""")
+    val reAS = Regex("""-?\d+\.?\d*\s*[+-]\s*[+-]?\d+\.?\d*""")
+    val reA  = Regex("""\d\+""")
+
+    while (true) {
+        val match = reMD.find(t)
+        if (match == null) break
+        val exp = match.value
+        val match2 = reM.find(exp)
+        t = if (match2 != null)
+                t.replace(exp, multiply(exp))
+            else
+                t.replace(exp, divide(exp))
+    }
+
+    while (true) {
+        val match = reAS.find(t)
+        if (match == null) break
+        val exp = match.value
+        val match2 = reA.find(exp)
+        t = if (match2 != null)
+                t.replace(exp, add(exp))
+            else
+                t.replace(exp, subtract(exp))
+    }
+
+    return t
+}
+
+fun evalArithmeticExp(s: String): Double {
+    var t = s.replace(Regex("""\s"""), "").replace("""^\+""", "")
+    val rePara = Regex("""\([^()]*\)""")
+    while(true) {
+        val match = rePara.find(t)
+        if (match == null) break
+        val exp = match.value
+        t = t.replace(exp, evalExp(exp))
+    }
+    return evalExp(t).toDoubleOrZero()
+}
+
+fun main(arsg: Array<String>) {
+    listOf(
+        "2+3",
+        "2+3/4",
+        "2*3-4",
+        "2*(3+4)+5/6",
+        "2 * (3 + (4 * 5 + (6 * 7) * 8) - 9) * 10",
+        "2*-3--4+-0.25",
+         "-4 - 3",
+         "((((2))))+ 3 * 5",
+         "1 + 2 * (3 + (4 * 5 + 6 * 7 * 8) - 9) / 10",
+         "1 + 2*(3 - 2*(3 - 2)*((2 - 4)*5 - 22/(7 + 2*(3 - 1)) - 1)) + 1"
+    ).forEach { println("$it = ${evalArithmeticExp(it)}") }
+}