|
1 | | -# CodingProblems |
| 1 | +# Coding Challenges |
| 2 | +### This repository contains various coding challenges taken on Sites like HackerRank, LeetCode etc. |
| 3 | + |
| 4 | +## Challenge#1- Prefix Notation |
| 5 | +#### Write a function that evaluates an expression written in Prefix Notiation and returrns a value |
| 6 | + |
| 7 | +##### Problem Statement: |
| 8 | + |
| 9 | +Prefix notation (also known as polish notation) is an alternative to the more familier infix notation. |
| 10 | + |
| 11 | +In infix notation, operators(add,multiply,etc) are written between their operands(number, variables, or sub-expression). |
| 12 | +* In prefix notation, operators are written before their operands |
| 13 | +Some examples follow of expression in infix notation and their equivalents in prefix notation. |
| 14 | +In this example the operator is + and its operands are 1 and 2: |
| 15 | + |
| 16 | +``` |
| 17 | +Infix expression: 1 + 2 |
| 18 | +Prefix expression: + 1 2 |
| 19 | +Value: 3 |
| 20 | +``` |
| 21 | + |
| 22 | +In this example, the sub-expression + 1 2 is the first operand of the + operator |
| 23 | + |
| 24 | +``` |
| 25 | +Infix expression: (1+2) * 3 |
| 26 | +Prefix expression: * + 1 2 3 |
| 27 | +Value: 9 |
| 28 | +``` |
| 29 | + |
| 30 | +Sometimes there are multiple sub-expressions: |
| 31 | +``` |
| 32 | +Infix expression: ((1 + 2) *3)-4 |
| 33 | +Prefix expression: - * + 1 2 3 4 |
| 34 | +value: 5 |
| 35 | +``` |
| 36 | + |
| 37 | +Sub-expressions can be nested arbitrarily deeply: |
| 38 | +``` |
| 39 | +Infix expression: 6 + (( 4 - (2 + 3 ) ) * 8 ) |
| 40 | +Prefix expression: + 6 * - 4 + 2 3 8 |
| 41 | +value: -2 |
| 42 | +``` |
| 43 | +##### Variables |
| 44 | +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. |
| 45 | + |
| 46 | +For example: |
| 47 | +``` |
| 48 | +expression: + 10 x |
| 49 | +variables {"x":3} |
| 50 | +value: 13 |
| 51 | +``` |
| 52 | +##### Task |
| 53 | + |
| 54 | +Implement a function CalculateExpression(expression,variables) |
| 55 | +that takes as inputs: |
| 56 | +* expression, a string containing an expression in prefix notiation that might contain variables |
| 57 | +* variables, a JSON objeect containing the values for each variable in the expression |
| 58 | +and returns: |
| 59 | +* the result of the expression for the given values |
| 60 | +* throw exception the expression is invalid or if the expression does not have any valid result |
| 61 | + |
| 62 | +The syntax supports 4 operators: +, -, *, and /. These are the standard artihmetic operators. |
| 63 | +* Note: / denotes integer division, that is / 7 2 evaluates to 3, not 3.5. |
| 64 | + |
| 65 | +The only accepted numeric operands aer positive integers in base 10 (e.g 1,22, 85 are valid, -1,0x43, 0 are not valid). |
| 66 | + |
| 67 | +A valid variable name is any sequence of characters that doesn't include whitespaces(spaces,tabs, newlines, etc). |
| 68 | + |
| 69 | +##### Examples |
| 70 | + |
| 71 | +``` |
| 72 | +Expression: + 1 5 |
| 73 | +variables: {} |
| 74 | +result: 6 |
| 75 | +``` |
| 76 | + |
| 77 | +``` |
| 78 | +Expression: + 1 2 3 |
| 79 | +variables: {} |
| 80 | +result: 6 |
| 81 | +``` |
| 82 | + |
| 83 | +``` |
| 84 | +Expression: + 1 |
| 85 | +variables: {} |
| 86 | +result: exception |
| 87 | +``` |
| 88 | + |
| 89 | +``` |
| 90 | +Expression: 9 |
| 91 | +variables: {} |
| 92 | +result: 9 |
| 93 | +``` |
| 94 | + |
| 95 | +``` |
| 96 | +Expression: * + 1 2 3 |
| 97 | +variables: {} |
| 98 | +result: 9 |
| 99 | +``` |
| 100 | + |
| 101 | +Although, negative numeric operands are invalid in expression, intermediate and final results may be negative |
| 102 | +``` |
| 103 | +Expression: + 6 * - 4 + 2 3 8 |
| 104 | +variables: {} |
| 105 | +result: -2 |
| 106 | +``` |
| 107 | + |
| 108 | +Operators and operrands must be seperated by one or more white spaces: |
| 109 | +``` |
| 110 | +Expression: -+1 5 3 |
| 111 | +variables: {} |
| 112 | +result: exception |
| 113 | +``` |
| 114 | + |
| 115 | +``` |
| 116 | +Expression: +1 2 |
| 117 | +variables: {} |
| 118 | +result: 3 |
| 119 | +``` |
| 120 | +Expression containing variables: |
| 121 | + |
| 122 | +``` |
| 123 | +Expression: * + 2 x y |
| 124 | +variables: {"x":1,"y":3} |
| 125 | +result: 9 |
| 126 | +``` |
| 127 | + |
| 128 | +##### Solution: CodingChallenge.HackerRank/PrefixNotation.cs |
| 129 | +##### Test Cases : CodingChallenge.Tests/UT_PrefixNotation.cs |
| 130 | + |
| 131 | + |
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