Add 150. Evaluate Reverse Polish Notation solution

Author: Rion5

LeetCode/EvaluateReversePolishNotation.cs

@@ -0,0 +1,80 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using Microsoft.VisualBasic.CompilerServices;
+
+namespace LeetCodeSolutionsLib
+{
+ /// <summary>
+ /// 150. Evaluate Reverse Polish Notation
+ /// Evaluate the value of an arithmetic expression in Reverse Polish Notation
+ /// Valid Operators are + - * /
+ /// IE) Input : ["2", "1", "+", "3", "*"]
+ /// Output : 9
+ /// Explanation: ((2 + 1) * 3) = 9
+ /// </summary>
+ public class EvaluateReversePolishNotation : Solution
+ {
+ private string[] _inputString;
+
+ public EvaluateReversePolishNotation(string[] tokens)
+ {
+ this._inputString = tokens;
+ }
+
+ private int evaluateReversePolishNotation(string[] tokens)
+ {
+ // Using a Stack, loop through each string in 'tokens' array
+ // 1) If element is a number, push it on top the stack
+ // 2) If element is an operator, pop two numbers from the stack, do the correct calculations and push back the results.
+ // Time Complexity : O(n) where n is the size of the token's array
+ // Space Complexity: O(n)
+ string validOperators = "+-*/";
+ Stack<int> stack = new Stack<int>();
+ int number = 0;
+ foreach (var element in tokens)
+ {
+ // 1)
+ if (int.TryParse(element, out number))
+ {
+ stack.Push(number);
+ }
+ // 2)
+ else
+ {
+ int rightValue = stack.Pop();
+ int leftValue = stack.Pop();
+ int operatorIndex = validOperators.IndexOf(element);
+ // Console.WriteLine($"{leftValue} {element.ToString()} {rightValue}");
+ switch (operatorIndex)
+ {
+ case 0:
+ stack.Push(leftValue + rightValue);
+ break;
+ case 1:
+ stack.Push(leftValue - rightValue);
+ break;
+ case 2:
+ stack.Push(leftValue * rightValue);
+ break;
+ case 3:
+ stack.Push(leftValue / rightValue);
+ break;
+ }
+ }
+ }
+ return stack.Pop();
+ }
+ public override void PrintExample()
+ {
+ var watch = System.Diagnostics.Stopwatch.StartNew();
+ var results = evaluateReversePolishNotation(this._inputString);
+ watch.Stop();
+ Console.WriteLine($"150. Evaluate Reverse Polish Notation\n" +
+ $"Input String = {printInputArray(this._inputString)} \n" +
+ $"Result: [{results}] \n" +
+ $"Execution Speed: {watch.ElapsedMilliseconds}ms \n");
+ }
+ }
+}

LeetCodeConsoleApp/Program.cs

@@ -83,6 +83,13 @@ static void Main(string[] args)
 
  #endregion
 
+ #region 150. Evaluate Reverse Polish Notation
+
+ EvaluateReversePolishNotation evaluateReversePolishNotation = new EvaluateReversePolishNotation(new []{ "2", "1", "+", "3", "*" });
+ evaluateReversePolishNotation.PrintExample();
+
+ #endregion
+
  #region 155. Min Stack
 
  MinStack minStack = new MinStack();