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feat: add algorithm to evaluate postfix string #1441
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raklaptudirm
merged 11 commits into
TheAlgorithms:master
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gaurovgiri:feat/evaluate-postfix-string
Oct 10, 2023
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032b28f
feat: add algorithm to evaluate postfix strings
gaurovgiri 83fae75
feat: add test case for evaluate expression
gaurovgiri ed1b831
update: add literature reference
gaurovgiri 0f418b0
fix: import name in testcase
gaurovgiri 23034da
fix: test case result
gaurovgiri 409fbec
Make clear that this is postfix
appgurueu 5105fe9
Update tests
appgurueu d45ef6d
Merge branch 'TheAlgorithms:master' into feat/evaluate-postfix-string
gaurovgiri 4fd461f
add: see reference
gaurovgiri 9c790bc
fixes mentioned issues
gaurovgiri f0ee63c
Fix `default` case
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,58 @@ | ||
| /** | ||
| * Evaluate a numeric operations string in postfix notation using a stack. | ||
| * Supports basic arithmetic operations: +, -, *, / | ||
| * @see https://www.geeksforgeeks.org/evaluation-of-postfix-expression/ | ||
| * @param {string} expression - Numeric operations expression to evaluate. Must be a valid postfix expression. | ||
| * @returns {number|null} - Result of the expression evaluation, or null if the expression is invalid. | ||
| */ | ||
| function evaluatePostfixExpression(expression) { | ||
| const stack = []; | ||
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| // Helper function to perform an operation and push the result to the stack. Returns success. | ||
| function performOperation(operator) { | ||
| const rightOp = stack.pop(); // Right operand is the top of the stack | ||
| const leftOp = stack.pop(); // Left operand is the next item on the stack | ||
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| if (leftOp === undefined || rightOp === undefined) { | ||
| return false; // Invalid expression | ||
| } | ||
| switch (operator) { | ||
| case '+': | ||
| stack.push(leftOp + rightOp); | ||
| break; | ||
| case '-': | ||
| stack.push(leftOp - rightOp); | ||
| break; | ||
| case '*': | ||
| stack.push(leftOp * rightOp); | ||
| break; | ||
| case '/': | ||
| if (rightOp === 0) { | ||
| return false; | ||
| } | ||
| stack.push(leftOp / rightOp); | ||
| break; | ||
| default: | ||
| return false; // Unknown operator | ||
| } | ||
| return true; | ||
| } | ||
|
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| const tokens = expression.split(/\s+/); | ||
|
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| for (const token of tokens) { | ||
| if (!isNaN(parseFloat(token))) { | ||
| // If the token is a number, push it to the stack | ||
| stack.push(parseFloat(token)); | ||
| } else { | ||
| // If the token is an operator, perform the operation | ||
| if (!performOperation(token)) { | ||
| return null; // Invalid expression | ||
| } | ||
| } | ||
| } | ||
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| return (stack.length === 1) ? stack[0] : null; | ||
| } | ||
|
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| export { evaluatePostfixExpression }; |
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,22 @@ | ||
| import { evaluatePostfixExpression } from '../EvaluateExpression.js'; | ||
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| describe('evaluatePostfixExpression', () => { | ||
| it('should evaluate a valid expression', () => { | ||
| const expression = '3 4 * 2 / 5 +'; // (3 * 4) / 2 + 5 = 11 | ||
| const result = evaluatePostfixExpression(expression); | ||
| expect(result).toBe(11); | ||
| }); | ||
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| it('should handle division by zero', () => { | ||
| const expression = '3 0 /'; // Division by zero | ||
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|
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| const result = evaluatePostfixExpression(expression); | ||
| expect(result).toBe(null); | ||
| }); | ||
|
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| it('should handle an invalid expression', () => { | ||
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|
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| const expression = '3 * 4 2 / +'; // Invalid expression | ||
| const result = evaluatePostfixExpression(expression); | ||
| expect(result).toBe(null); | ||
| }); | ||
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| }); | ||
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