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

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  • 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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