LeetCode Entry

150. Evaluate Reverse Polish Notation

30.01.2024 medium 2024 kotlin rust

Solve Reverse Polish Notation.

150. Evaluate Reverse Polish Notation medium blog post substack youtube image.png

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Problem TLDR

Solve Reverse Polish Notation.

Intuition

Push to stack until operation met, then pop twice and do op.

Approach

Let’s try to be brief.

Complexity

  • Time complexity: \(O(n)\)

  • Space complexity: \(O(n)\)

Code


  fun evalRPN(tokens: Array<String>) = Stack<Int>().run {
    for (s in tokens) push(when (s) {
      "+" -> pop() + pop()
      "-" -> -pop() + pop()
      "*" -> pop() * pop()
      "/" -> pop().let { pop() / it }
      else -> s.toInt()
    })
    pop()
  }



  pub fn eval_rpn(tokens: Vec<String>) -> i32 {
    let mut s = vec![];
    for t in tokens { if let Ok(n) = t.parse() { s.push(n) }
     else { let (a, b) = (s.pop().unwrap(), s.pop().unwrap());
      s.push(match t.as_str() {
        "+" => a + b, "-" => b - a, "*" => a * b, _ => b / a }) }}
    s[0]
  }