150 / Evaluate Reverse Polish Notation / Medium / 36m 44s

Author: oris8

oris8/150_evaluate-reverse-polish-notation.js

@@ -0,0 +1,29 @@
+/**
+ *
+ * 150 / Evaluate Reverse Polish Notation / Medium / 36m 44s
+ *
+ * @param {string[]} tokens
+ * @return {number}
+ */
+var evalRPN = function (tokens) {
+  const operators = {
+    "+": (a, b) => a + b,
+    "-": (a, b) => a - b,
+    "*": (a, b) => a * b,
+    "/": (a, b) => Math.trunc(a / b),
+  };
+
+  const stack = [];
+
+  for (const token of tokens) {
+    if (operators?.[token]) {
+      const b = stack.pop();
+      const a = stack.pop();
+      stack.push(operators[token](a, b));
+    } else {
+      stack.push(+token);
+    }
+  }
+
+  return stack.pop();
+};