227. Basic Calculator II

Author: VinayByte

227. Basic Calculator II.kt

@@ -0,0 +1,30 @@
+class Solution {
+    fun calculate(s: String): Int {
+        val stack = mutableListOf<Int>()
+        var num = 0
+        var sign = '+'
+
+        for (char in s) {
+            if (char.isDigit()) {
+                num = num * 10 + (char - '0')
+            } else if (char != ' ') {
+                when (sign) {
+                    '+' -> stack.add(num)
+                    '-' -> stack.add(-num)
+                    '*' -> stack.add(stack.removeAt(stack.size - 1) * num)
+                    '/' -> stack.add(stack.removeAt(stack.size - 1) / num)
+                }
+                sign = char
+                num = 0
+            }
+        }
+
+        when (sign) {
+            '+' -> stack.add(num)
+            '-' -> stack.add(-num)
+            '*' -> stack.add(stack.removeAt(stack.size - 1) * num)
+            '/' -> stack.add(stack.removeAt(stack.size - 1) / num)
+        }
+        return stack.sum()
+    }
+}