Merge branch 'main' of https://github.com/csehammad/CodingProblems into main

csehammad · csehammad · commit 56bd743645a5 · 2021-11-25T02:00:02.000+05:00
diff --git a/README.md b/README.md
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-# CodingProblems
+# Coding Challenges 
+### This repository contains various coding challenges taken on Sites like HackerRank, LeetCode etc. 
+
+## Challenge#1- Prefix Notation 
+#### Write a function that evaluates an expression written in Prefix Notiation and returrns a value 
+
+##### Problem Statement: 
+
+Prefix notation (also known as polish notation) is an alternative to the more familier infix notation. 
+
+In infix notation, operators(add,multiply,etc) are written between their operands(number, variables, or sub-expression). 
+* In prefix notation, operators are written before their operands
+Some examples follow of expression in infix notation and their equivalents in prefix notation. 
+In this example the operator is + and its operands are 1 and 2:
+
+```
+Infix expression: 1 + 2 
+Prefix expression: + 1 2 
+Value: 3
+```
+
+In this example, the sub-expression + 1 2 is the first operand of the + operator 
+
+```
+Infix expression: (1+2) * 3
+Prefix expression: * + 1 2 3 
+Value: 9 
+```
+
+Sometimes there are multiple sub-expressions:
+``` 
+Infix expression: ((1 + 2) *3)-4 
+Prefix expression: - * + 1 2 3 4
+value: 5
+``` 
+
+Sub-expressions can be nested arbitrarily deeply:
+``` 
+Infix expression: 6 + (( 4 - (2 + 3 ) ) * 8 )
+Prefix expression: + 6 * - 4 + 2 3 8
+value: -2
+``` 
+##### Variables
+So far we have only considered numbers as our operands for the prefix expression. For this test, we would like your function to also support variables withing the expression. 
+
+For example: 
+``` 
+expression: + 10 x 
+variables {"x":3}
+value: 13
+```
+##### Task
+
+Implement a function CalculateExpression(expression,variables)
+that takes as inputs:
+* expression, a string containing an expression in prefix notiation that might contain variables 
+* variables, a JSON objeect containing the values for each variable in the expression
+and returns: 
+* the result of the expression for the given values 
+* throw exception the expression is invalid or if the expression does not have any valid result
+
+The syntax supports 4 operators: +, -, *, and /. These are the standard artihmetic operators.
+* Note: / denotes integer division, that is / 7 2 evaluates to 3, not 3.5. 
+
+The only accepted numeric operands aer positive integers in base 10 (e.g 1,22, 85 are valid, -1,0x43, 0 are not valid).
+
+A valid variable name is any sequence of characters that doesn't include whitespaces(spaces,tabs, newlines, etc). 
+
+##### Examples
+
+```
+Expression: + 1 5
+variables: {}
+result: 6
+```
+
+```
+Expression: + 1 2 3
+variables: {}
+result: 6
+```
+
+```
+Expression: + 1
+variables: {}
+result: exception
+```
+
+```
+Expression: 9
+variables: {}
+result: 9
+```
+
+```
+Expression: * + 1 2 3
+variables: {}
+result: 9
+```
+
+Although, negative numeric operands are invalid in expression, intermediate and final results may be negative
+```
+Expression: + 6 * - 4 + 2 3 8 
+variables: {}
+result: -2
+```
+
+Operators and operrands must be seperated by one or more white spaces:
+```
+Expression: -+1 5 3
+variables: {}
+result: exception
+```
+ 
+```
+Expression: +1       2
+variables: {}
+result: 3
+```
+Expression containing variables:
+
+```
+Expression: * + 2 x y
+variables: {"x":1,"y":3}
+result: 9
+```
+
+##### Solution: CodingChallenge.HackerRank/PrefixNotation.cs
+##### Test Cases : CodingChallenge.Tests/UT_PrefixNotation.cs
+
+
