Feat | NeetCode | Roadmap | #23 Evaluate Reverse Polish Potation

README.md

@@ -94,4 +94,5 @@
   - [Task #20](src/neetcode/sliding-window/sliding-window-maximum) – _Sliding Window Maximum_ - _[check the task](https://neetcode.io/problems/sliding-window-maximum)_
 - Stack
   - [Task #21](src/neetcode/stack/valid-parentheses) – _Valid Parentheses_ - _[check the task](https://leetcode.com/problems/valid-parentheses)_
-  - [Task #22](src/neetcode/stack/min-stack) – _Min Stack_ - _[check the task](https://leetcode.com/problems/minimum-stack)_
+  - [Task #22](src/neetcode/stack/min-stack) – _Min Stack_ - _[check the task](https://leetcode.com/problems/minimum-stack)_
+  - [Task #23](src/neetcode/stack/evaluate-reverse-polish-notation) – _Evaluate Reverse Polish Notation_ - _[check the task](https://neetcode.io/problems/evaluate-reverse-polish-notation)_

src/neetcode/stack/evaluate-reverse-polish-notation/solution.test.ts

@@ -0,0 +1,35 @@
+import { evalRPN } from './solution';
+
+describe('Evaluate Reverse Polish Notation | NeetCode | RoadMap | Testcases', () => {
+  test('#1 Evaluates multiplication after addition', () => {
+    const tokens = ['2', '1', '+', '3', '*', '4', '-'];
+    const expected = 5;
+    const output = evalRPN(tokens);
+
+    expect(output).toBe(expected);
+  });
+
+  test('#2 Evaluates division and addition', () => {
+    const tokens = ['4', '13', '5', '/', '+'];
+    const expected = 6;
+    const output = evalRPN(tokens);
+
+    expect(output).toBe(expected);
+  });
+
+  test('#3 Evaluates a complex expression', () => {
+    const tokens = ['10', '6', '9', '3', '+', '-11', '*', '/', '*', '17', '+', '5', '+'];
+    const expected = 22;
+    const output = evalRPN(tokens);
+
+    expect(output).toBe(expected);
+  });
+
+  test('#4 Truncates division toward zero', () => {
+    const tokens = ['-7', '3', '/'];
+    const expected = -2;
+    const output = evalRPN(tokens);
+
+    expect(output).toBe(expected);
+  });
+});

src/neetcode/stack/evaluate-reverse-polish-notation/solution.ts

@@ -0,0 +1,46 @@
+type Operators = '+' | '-' | '*' | '/';
+/**
+ * @param {string[]} tokens
+ * @return {number}
+ */
+export const evalRPN = (tokens: string[]): number => {
+  const stack: number[] = [];
+  const operators: Record<string, Operators | undefined> = {
+    '+': '+',
+    '-': '-',
+    '*': '*',
+    '/': '/',
+  };
+
+  for (const t of tokens) {
+    const op = operators[t];
+    if (op !== undefined) {
+      const b = stack.pop();
+      const a = stack.pop();
+      if (a !== undefined && b !== undefined) {
+        switch (op) {
+          case '+': {
+            stack.push(a + b);
+            break;
+          }
+          case '-': {
+            stack.push(a - b);
+            break;
+          }
+          case '*': {
+            stack.push(a * b);
+            break;
+          }
+          case '/': {
+            stack.push(Math.trunc(a / b));
+            break;
+          }
+        }
+      }
+    } else {
+      stack.push(Number(t));
+    }
+  }
+
+  return stack.pop() ?? -1;
+};