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How to find the Entry with largest Key in a Java Map

Last Updated : 19 Jul, 2022
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Given a map in Java, the task is to find out the entry in this map with the highest key. Examples:

Input: Map = {ABC = 10, DEF = 30, XYZ = 20}
Output: XYZ = 20

Input: Map = {1 = 40, 2 = 30, 3 = 60}
Output: 3 = 60

Approach

  1. Iterate the map entry by entry
for (Map.Entry entry : map.entrySet()) 
{
    // Operations
}
  1. Store the first entry in a reference variable to compare to initially.
  2. If the current entry's key is greater than the reference entry's value, then store the current entry as the reference entry.
  3. Repeat this process for all the entries in the map.
  4. In the end, the reference variable has the required entry with the highest key in the map.
  5. Print this entry

Below is the implementation of the above approach: 

Java
// Java program to find entry 
// with highest key in a map 

import java.util.*; 

public class GFG { 

    // Find the entry with highest key 
    public static <K extends Comparable<K>, V> Map.Entry<K, V> 
    getMaxEntryInMapBasedOnKey(Map<K, V> map) 
    { 
        // To store the result 
        Map.Entry<K, V> entryWithMaxKey = null; 

        // Iterate in the map to find the required entry 
        for (Map.Entry<K, V> currentEntry : map.entrySet()) { 

            if ( 

                // If this is the first entry, 
                // set the result as this 
                entryWithMaxKey == null

                // If this entry's key is more than the max key 
                // Set this entry as the max 
                || currentEntry.getKey() 
                        .compareTo(entryWithMaxKey.getKey()) 
                    > 0) { 

                entryWithMaxKey = currentEntry; 
            } 
        } 

        // Return the entry with highest key 
        return entryWithMaxKey; 
    } 

    // Print the map 
    public static void print(Map<String, Integer> map) 
    { 

        System.out.print("Map: "); 

        // If map does not contain any value 
        if (map.isEmpty()) { 
            System.out.println("[]"); 
        } 

        else { 
            System.out.println(map); 
        } 
    } 

    // Driver code 
    public static void main(String[] args) 
    { 

        Map<String, Integer> map 
            = new HashMap<>(); 
        map.put("ABC", 10); 
        map.put("DEF", 30); 
        map.put("XYZ", 20); 

        print(map); 

        System.out.println( 
            "Entry with highest key: "
            + getMaxEntryInMapBasedOnKey(map)); 
    } 
} 
Output:
Map: {ABC=10, DEF=30, XYZ=20}
Entry with highest key: XYZ=20

Time complexity: O(NlogN) where N is size of map

Auxiliary Space: O(N)


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