LeetCode 227: Basic Calculator II

Given a string that contains digits and '+-*/' presenting a valid expression, implement a basic calculator to evaluate it. Use a variable tempResult to save the intermediate result. When we encounter '+', '-', '*' or '/'operators , evaluate the expression to the left of the previous operator. Add tempResult to final result if previous operator is '+' or '-' . Multiply or divide tempResult by the operand if previous operator is '*' or ‘/ respectively.

Basic calculator II summary card

Table of Contents

· String consists of digits, '+' , '-', '∗' and '/'
  ∘ Graph Explanation
  ∘ Code Implementation
   ∘ Golang
   ∘ Python

String consists of digits, '+' , '-', '∗' and '/'

227. Basic Calculator II

Example:
Input: "10 + 2*3 - 6/3"
Output: 14

According the order of operations, we should perform multiplication and division first. Therefore, we aren’t able to evaluate the expression to the left immediately once we encounter '+', '-', '*' or '/'operators.

Instead, we use a variable tempResult to save the intermediate result and evaluate the expression to the left of the previous operator as we met a '+', '-', '*' or '/'operator.

• If the previous operator is '+' or '-' , we add tempResult to final result.
• If the previous operator is '*', we multiply tempResult by the operand.
• If the previous operator is '/', we divide tempResult by the operand.

string consists +-*/

Graph Explanation

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Code Implementation

• Complexity
  Time: O(n) one pass
  Space: O(1)
  n: the length of the string expression

Golang

Python

You can access the source code here.

LeetCode Questions:

• 227. Basic Calculator II

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