Sort an Array of dates in ascending order using Custom Comparator

Difficulty Level : Easy
Last Updated : 02 Dec, 2020

Given an array arr[] of N dates in the form of “DD-MM-YYYY”, the task is to sort these dates in ascending order.

Examples:

Input: arr[] = { “25-08-1996”, “03-08-1970”, “09-04-1994” }
Output:
03-08-1970
09-04-1994
25-08-1996

Input: arr[] = { “03-08-1970”, “09-04-2020”, “19-04-2019″”}
Output:
03-08-1970
19-04-2019
09-04-2020

Approach:

Create a Custom comparator function that compares two dates as below:
- First compare the year of the two elements. The element with greater year will come after the other element.
- If the year of both the dates is same then compare the months. The element with a greater month will come after the other element.
- If the month of both the dates is same then compare the dates. The element with greater date will come after the other element.
Then sort the array using the defined custom comparator. In C++, it is done as:

sort(initial position, ending position, comparator)

Print the modified array.

Below is the implementation of the above approach:

C++

// C++ implementation to sort the
// array of dates in the form of
// "DD-MM-YYYY" using custom comparator
 
#include <bits/stdc++.h>
using namespace std;
 
// Comparator to sort the array of dates
int myCompare(string date1,
              string date2)
{
    string day1 = date1.substr(0, 2);
    string month1 = date1.substr(3, 2);
    string year1 = date1.substr(6, 4);
 
    string day2 = date2.substr(0, 2);
    string month2 = date2.substr(3, 2);
    string year2 = date2.substr(6, 4);
 
    // Condition to check the year
    if (year1 < year2)
        return 1;
    if (year1 > year2)
        return 0;
 
    // Condition to check the month
    if (month1 < month2)
        return 1;
    if (month1 > month2)
        return 0;
 
    // Condition to check the day
    if (day1 < day2)
        return 1;
    if (day1 > day2)
        return 0;
}
 
// Function that prints the
// dates in ascensding order
void printDatesAscending(
    vector<string> arr)
{
    // Sort the dates using library
    // sort function with custom Comparator
    sort(arr.begin(), arr.end(), myCompare);
 
    // Loop to print the dates
    for (int i = 0; i < arr.size(); i++)
        cout << arr[i] << "\n";
}
 
// Driver Code
int main()
{
    vector<string> arr;
    arr.push_back("25-08-1996");
    arr.push_back("03-08-1970");
    arr.push_back("09-04-1994");
    arr.push_back("29-08-1996");
    arr.push_back("14-02-1972");
 
    printDatesAscending(arr);
 
    return 0;
}

Java

// Java implementation to sort the 
// array of dates in the form of 
// "DD-MM-YYYY" using custom comparator 
import java.util.*;
import java.lang.*;
 
class GFG{
     
// Function that prints the 
// dates in ascensding order 
static void printDatesAscending(ArrayList<String> arr) 
{ 
     
    // Sort the dates using library 
    // sort function with custom Comparator 
    Collections.sort(arr,new Comparator<>()
    {
        public int compare(String date1, String date2)
        {
            String day1 = date1.substring(0, 2); 
            String month1 = date1.substring(3, 5); 
            String year1 = date1.substring(6); 
           
            String day2 = date2.substring(0, 2); 
            String month2 = date2.substring(3, 5); 
            String year2 = date2.substring(6); 
             
            // Condition to check the year 
            if (year2.compareTo(year1) > 0)
                return -1;
            else if (year2.compareTo(year1) < 0)
                return 1;
             
            // Condition to check the month     
            else if (month2.compareTo(month1) > 0)
                return -1;
            else if (month2.compareTo(month1) < 0)
                return 1;
             
            // Condition to check the day 
            else if (day2.compareTo(day1) > 0)
                return -1;
            else
                return 1;
        }
    }); 
     
    // Loop to print the dates 
    for(int i = 0; i < arr.size(); i++) 
        System.out.println(arr.get(i)); 
}  
 
// Driver code
public static void main(String[] args) 
{
    ArrayList<String> arr = new ArrayList<>(); 
    arr.add("25-08-1996"); 
    arr.add("03-08-1970"); 
    arr.add("09-04-1994"); 
    arr.add("29-08-1996"); 
    arr.add("14-02-1972"); 
     
    printDatesAscending(arr); 
}
}
 
// This code is contributed by offbeat

Output:

Time Complexity: O(N*log N)

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