PHP | Number of week days between two dates

You are given two string (dd-mm-yyyy) representing two date, you have to find number of all weekdays present in between given dates.(both inclusive) Examples:

Input : startDate = "01-01-2018"   endDate = "01-03-2018"
Output : Array
(
    [Monday] => 9
    [Tuesday] => 9
    [Wednesday] => 9
    [Thursday] => 9
    [Friday] => 8
    [Saturday] => 8
    [Sunday] => 8
)

Input : startDate = "01-01-2018"   endDate = "01-01-2018"
Output : Array
(
    [Monday] => 1
    [Tuesday] => 0
    [Wednesday] => 0
    [Thursday] => 0
    [Friday] => 0
    [Saturday] => 0
    [Sunday] => 0
)

The basic idea to find out number of all weekdays is very simple, you have to iterate from start date to end date and increase the count of each day. Hence you can calculate the desired result. In php we can find day for a particular date by using date() function as date(‘l’, $timestamp) where $timestamp is the value of strtotime($date). Also you can increase the date value by 1 with the help of $date->modify(‘+1 day’). Algorithm :

convert startDate & endDate string into Datetime() object. Iterate from startDate to endDate in a loop: Find out then  timestamp of startDate.Find out the weekday for current timestamp of startDate.Increase the value of particular weekday by 1.Increase the value of startDate by 1.Print the array containing value of all weekdays.

PHP

<?php
    // input start and end date
    $startDate = "01-01-2018";
    $endDate = "01-01-2019";

    $resultDays = array('Monday' => 0,
    'Tuesday' => 0,
    'Wednesday' => 0,
    'Thursday' => 0,
    'Friday' => 0,
    'Saturday' => 0,
    'Sunday' => 0);

    // change string to date time object
    $startDate = new DateTime($startDate);
    $endDate = new DateTime($endDate);

    // iterate over start to end date
    while($startDate <= $endDate ){
        // find the timestamp value of start date
        $timestamp = strtotime($startDate->format('d-m-Y'));

        // find out the day for timestamp and increase particular day
        $weekDay = date('l', $timestamp);
        $resultDays[$weekDay] = $resultDays[$weekDay] + 1;

        // increase startDate by 1
        $startDate->modify('+1 day');
    }

    // print the result
    print_r($resultDays);
?>

Output :

Array
(
    [Monday] => 53
    [Tuesday] => 53
    [Wednesday] => 52
    [Thursday] => 52
    [Friday] => 52
    [Saturday] => 52
    [Sunday] => 52
)

Time Complexity : O(n)

Space Complexity : O(1)