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Fix DateToDay #1126

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sharansukesh1003 wants to merge 10 commits into TheAlgorithms:master from sharansukesh1003:master
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39 changes: 9 additions & 30 deletions Conversions/DateToDay.js
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Original file line number Diff line number Diff line change
Expand Up @@ -4,30 +4,11 @@
The DateToDay method takes a date in string format and
returns the name of a day. The approach behind this method
is very simple, we first take a string date and check
whether their date is valid or not, if the date is valid
then we do this But apply the algorithm shown below. The
algorithm shown below gives us the number of the day and
finally converts it to the name of the day.

Algorithm & Explanation : https://cs.uwaterloo.ca/~alopez-o/math-faq/node73.html
whether their date is valid or not, if the date is not valid
then we return a type error, else we apply Zeller's congruence.
Algorithm & Explanation : https://www.geeksforgeeks.org/zellers-congruence-find-day-date/
*/

// March is taken as the first month of the year.
const calcMonthList = {
1: 11,
2: 12,
3: 1,
4: 2,
5: 3,
6: 4,
7: 5,
8: 6,
9: 7,
10: 8,
11: 9,
12: 10
}

// show the week day in a number : Sunday - Saturday => 0 - 6
const daysNameList = { // weeks-day
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@appgurueu appgurueu Oct 7, 2022

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Please use an array here.

0: 'Sunday',
Expand All @@ -38,25 +19,23 @@ const daysNameList = { // weeks-day
5: 'Friday',
6: 'Saturday'
}

const DateToDay = (date) => {
// firstly, check that input is a string or not.
if (typeof date !== 'string') {
return new TypeError('Argument is not a string.')
}
// extract the date
const [day, month, year] = date.split('/').map((x) => Number(x))
let [day, month, year] = date.split('/').map((x) => Number(x))
// check the data are valid or not.
if (day < 0 || day > 31 || month > 12 || month < 0) {
return new TypeError('Date is not valid.')
}
// divide year to century and yearDigit value.
const yearDigit = (year % 100)
// date is resolved based on Zeller's congruence.
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@appgurueu appgurueu Oct 7, 2022

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That's the overarching comment. This should be specific to the following line: "Count Jan & Feb as months 13 & 14 of the previous year".

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@sharansukesh1003 sharansukesh1003 Oct 7, 2022

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Ohhh great input, I will change it.

if (month < 3) { year--; month += 12 }
const century = Math.floor(year / 100)
// Apply the algorithm shown above
const weekDay = Math.abs((day + Math.floor((2.6 * calcMonthList[month]) - 0.2) - (2 * century) + yearDigit + Math.floor(yearDigit / 4) + Math.floor(century / 4)) % 7)
// return the weekDay name.
return daysNameList[weekDay]
year %= 100
const weekDay = (year + Math.floor(year / 4) + Math.floor(century / 4) - 2 * century + Math.floor((26 * (month + 1)) / 10) + day - 1) % 7
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@appgurueu appgurueu Oct 8, 2022

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You don't need the % 7 here if you apply % 7 below.

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@sharansukesh1003 sharansukesh1003 Oct 8, 2022

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Hmmm understood, changed it.

return daysNameList[(weekDay + 7) % 7]
}

// Example : DateToDay("18/12/2020") => Friday
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4 changes: 2 additions & 2 deletions Conversions/test/DateToDay.test.js
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Original file line number Diff line number Diff line change
Expand Up @@ -2,7 +2,7 @@ import { DateToDay } from '../DateToDay'

test('The date 18/02/2001 is Monday', () => {
const res = DateToDay('18/02/2001')
expect(res).toBe('Monday')
expect(res).toBe('Sunday')
})

test('The date 18/12/2020 is Friday', () => {
Expand All @@ -16,5 +16,5 @@ test('The date 12/12/2012 is Wednesday', () => {
})
test('The date 01/01/2001 is Friday', () => {
const res = DateToDay('01/01/2001')
expect(res).toBe('Friday')
expect(res).toBe('Monday')
})

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