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Commit 430e7f3

Browse files
postfix-expression-evaluation knaxus#61
- Update test case for exception
1 parent a00df3e commit 430e7f3

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2 files changed

+78
-53
lines changed

2 files changed

+78
-53
lines changed

‎src/_DataStructures_/Stack/postfix-expression-evaluation/index.js‎

Lines changed: 45 additions & 28 deletions
Original file line numberDiff line numberDiff line change
@@ -6,39 +6,56 @@
66

77
const Stack = require('../index');
88

9+
const ERROR_STRING = 'Expression is not in order';
10+
911
function evaluatePostfixExpression(expression) {
10-
let s = new Stack();
11-
for (let i = 0; i < expression.length; i++) {
12-
const char = expression[i];
13-
if (!isNaN(char)) {
14-
//if number push the char onto stack
15-
s.push(Number(char));
16-
} else {
17-
// if char is an operator then pop two elements from stack, evaluate them accordingly based on operator.
18-
//push the result to stack
19-
let val1 = s.pop();
20-
let val2 = s.pop();
21-
switch (char) {
22-
case '+':
23-
s.push(val2 + val1);
24-
break;
25-
case '-':
26-
s.push(val2 - val1);
27-
break;
28-
case '*':
29-
s.push(val2 * val1);
30-
break;
31-
case '/':
32-
s.push(val2 / val1);
33-
break;
12+
// eslint-disable-next-line no-param-reassign
13+
expression = expression.trim();
14+
15+
if (expression.length === 0 || expression.length === 1) {
16+
return ERROR_STRING;
17+
}
3418

35-
}
36-
}
19+
const s = new Stack();
20+
// eslint-disable-next-line no-plusplus
21+
for (let i = 0; i < expression.length; i++) {
22+
const char = expression[i];
23+
// eslint-disable-next-line no-restricted-globals
24+
if (!isNaN(char)) {
25+
// if number push the char onto stack
26+
s.push(Number(char));
27+
} else {
28+
// if char is an operator then pop two elements from stack, evaluate them accordingly based on operator.
29+
// push the result to stack
30+
const val1 = s.pop();
31+
const val2 = s.pop();
32+
switch (char) {
33+
case '+':
34+
s.push(val2 + val1);
35+
break;
36+
case '-':
37+
s.push(val2 - val1);
38+
break;
39+
case '*':
40+
s.push(val2 * val1);
41+
break;
42+
case '/':
43+
s.push(val2 / val1);
44+
break;
45+
default:
46+
break;
47+
}
3748
}
38-
//pop the value of postfix expression
39-
return s.pop();
49+
}
50+
// pop the value from stack
51+
const result = s.pop();
52+
if (s.isEmpty()) {
53+
return result;
54+
}
55+
return ERROR_STRING;
4056
}
4157

4258
module.exports = {
4359
evaluatePostfixExpression,
60+
ERROR_STRING,
4461
};
Lines changed: 33 additions & 25 deletions
Original file line numberDiff line numberDiff line change
@@ -1,55 +1,63 @@
1-
const { evaluatePostfixExpression } = require('.');
1+
const { evaluatePostfixExpression,ERROR_STRING } = require('.');
22

3-
describe('Postfix expression evaluation', function() {
4-
it('should be a function', function() {
3+
describe('Postfix expression evaluation', ()=> {
4+
it('should be a function', ()=> {
55
expect(typeof evaluatePostfixExpression).toEqual('function');
66
});
7-
8-
it('should return a number', function() {
7+
8+
it('should return a number', ()=> {
99
const expression = '11+';
10-
11-
expect(typeof evaluatePostfixExpression(expression)).toEqual('number')
10+
11+
expect(typeof evaluatePostfixExpression(expression)).toEqual('number');
1212
});
13-
14-
it('should handle addition', function() {
13+
14+
it('should handle addition', ()=> {
1515
const expression = '23+';
1616
const expected = 5;
17-
17+
1818
expect(evaluatePostfixExpression(expression)).toEqual(expected);
1919
});
20-
21-
it('should handle subtraction', function() {
20+
21+
it('should handle subtraction', ()=> {
2222
const expression = '54-';
2323
const expected = 1;
24-
24+
2525
expect(evaluatePostfixExpression(expression)).toEqual(expected);
2626
});
27-
28-
it('should handle multiplication', function() {
27+
28+
it('should handle multiplication', ()=> {
2929
const expression = '34*';
3030
const expected = 12;
31-
31+
3232
expect(evaluatePostfixExpression(expression)).toEqual(expected);
3333
});
34-
35-
it('should handle division', function() {
34+
35+
it('should handle division', ()=> {
3636
const expression = '62/';
3737
const expected = 3;
38-
38+
3939
expect(evaluatePostfixExpression(expression)).toEqual(expected);
4040
});
41-
42-
it('should handle negative numbers', function() {
41+
42+
it('should handle negative numbers', ()=> {
4343
const expression = '25-';
4444
const expected = -3;
45-
45+
4646
expect(evaluatePostfixExpression(expression)).toEqual(expected);
4747
});
48-
49-
it('should handle multiple operators', function() {
48+
49+
it('should handle multiple operators', ()=> {
5050
const expression = '123*+';
5151
const expected = 7;
52-
52+
5353
expect(evaluatePostfixExpression(expression)).toEqual(expected);
5454
});
55+
56+
describe('should throw error on invalid expressions', () => {
57+
const invalidExpressions = ['12', '1', '+', '1+2', '+12'];
58+
test.each(invalidExpressions)('running for %p', (expression) => {
59+
const result = evaluatePostfixExpression(expression);
60+
expect(result).toEqual(ERROR_STRING);
61+
});
62+
});
5563
});

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