150. Evaluate Reverse Polish Notation

Evaluate an arithmetic expression in Reverse Polish Notation. Operators are +, −, *, /; division truncates toward zero.

Push numbers. On an operator, pop the right then the left operand, apply it, and push the result. The last value on the stack is the answer.

1function evalRPN(tokens: string[]): number {
2  const stack: number[] = [];
3  for (const tok of tokens) {
4    if (!["+", "-", "*", "/"].includes(tok)) { stack.push(+tok); continue; }
5    const b = stack.pop()!, a = stack.pop()!;
6    stack.push(tok === "+" ? a + b : tok === "-" ? a - b : tok === "*" ? a * b : Math.trunc(a / b));
7  }
8  return stack[0];
9}

tokens

stack (top = right)

empty

Empty stack.

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