Evaluate Reverse Polish Notation Medium 0 attempts
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Evaluate Reverse Polish Notation

Medium Stack&Queue LeetCode

You're given an arithmetic expression written in Reverse Polish (postfix) Notation as a list of tokens. Compute its value, where the supported operators are +, -, *, and /, and division between two integers truncates toward zero rather than rounding down.

Input Format
Implement evalRPN(tokens). Inputs below show JavaScript function arguments; there is no stdin parsing.
Output Format
Return the result described in the statement.

Sample Input and Output

Example 1 ยท Run Sample

Input
tokens = ["2","1","+","3","*"]
Output
9

Example 2

Input
tokens = ["4","13","5","/","+"]
Output
6
Constraints
  • 1 <= tokens.length <= 10^4
  • tokens[i] is an operator or integer in [-200, 200]
Test Cases (2)
Case 1
Args: [["2","1","+","3","*"]] Expected: 9
Case 2
Args: [["4","13","5","/","+"]] Expected: 6
Topics
Stack&Queue

Stack

javascript
function evalRPN(tokens) {
  const stack = [];
  for (const t of tokens) {
    if ('+-*/'.includes(t)) {
      const b = stack.pop(), a = stack.pop();
      if (t === '+') stack.push(a + b);
      else if (t === '-') stack.push(a - b);
      else if (t === '*') stack.push(a * b);
      else stack.push(Math.trunc(a / b));
    } else stack.push(Number(t));
  }
  return stack[0];
}

Time: O(n) | Space: O(n)

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JavaScript