CC-10 : Find most frequent integer after k.

Description:

Given an integer k and an array of integers arr, count the frequency of characters that occur immediately after index k in arr. Return the integer that occurs most frequently after k.

Test cases and expected outputs:

Input Parameters	Expected outputs
arr={2,3,2,4,2,2,3,2,1}; k=2;	Most Common Element after 2 is 3
arr={2,3,2,4,2,2,3,2,1,2,2,2}; k=2;	Most Common Element after 2 is 2

Pseudocode:

The java method should accept following input parameters: arr (integer array), k (integer).

Initialize a variable cntMap of type HashMap< Integer,Integer> to hold integers occurring immediately after k and their frequency of occurring in arr.

Initialize maxCnt to 0. Initialize maxInt to Integer.MIN_VALUE.

Iterate through arr using a for loop with idx as a loop variable with initial value 0 and increment idx till it reaches arr.length-1:

If cntMap does not contain key equal to arr[idx+1]:

Add key arr[idx+1] and add value 1 to cntMap.

If cntMap contains key equal to arr[idx+1]:

Add key arr[idx+1] and add value equal to current value of key arr[idx+1], incremented by 1 to cntMap.

If value corresponding to key arr[idx+1] is greater than maxCnt:

Set maxCnt= value corresponding to key arr[idx+1].

Set maxInt= arr[idx+1].

After above loop completes successfully, maxInt contains the most frequent integer after k in arr. Return maxInt.

Code:

public int hashMapMostFreqAfterKey(int[] arr, int k) throws Exception{
	HashMap< Integer,Integer> cntMap=new HashMap< Integer, Integer>();
	int maxCnt=0; int maxInt=Integer.MIN_VALUE;
	for (int idx=0; idx < arr.length; idx++) {
		if ((arr[idx]==k)&& (idx+1 < arr.length)){
			cntMap.put(arr[idx+1], cntMap.getOrDefault(arr[idx+1], 0)+1);
			if (cntMap.get(arr[idx+1]) > maxCnt) {
				maxCnt=cntMap.get(arr[idx+1]);
				maxInt=arr[idx+1];
			}
		}		
	}		
	return 	maxInt;
}

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Below fully running code can be copied and run on Eclipse or other Java IDEs. Refer the classname in code below. If the class name below is "A", save the code below to a file named A.java before running it. Be sure to try your own test cases to enhance your understanding ! You can also tweak the code to optimize or add enhancements and custom features.

import java.util.HashMap;


public class HashMapMostFrequentAfterKey {
	
public int hashMapMostFreqAfterKey(int[] arr, int k) throws Exception{
	HashMap< Integer,Integer> cntMap=new HashMap< Integer, Integer>();
	int maxCnt=0; int maxInt=Integer.MIN_VALUE;
	for (int idx=0; idx < arr.length; idx++) {
		if ((arr[idx]==k)&& (idx+1 < arr.length)){
			cntMap.put(arr[idx+1], cntMap.getOrDefault(arr[idx+1], 0)+1);
			if (cntMap.get(arr[idx+1]) > maxCnt) {
				maxCnt=cntMap.get(arr[idx+1]);
				maxInt=arr[idx+1];
			}
		}		
	}		
	return 	maxInt;
}
	
	
    
public static void main(String[] args) {
		
	HashMapMostFrequentAfterKey hp=new HashMapMostFrequentAfterKey();
	int retVal;
	try {
	int[] arr1={2,3,2,4,2,2,3,2,1};
	int k=2;
	printArraySummary(arr1, "The input array");
	retVal=hp.hashMapMostFreqAfterKey(arr1,k);
	System.out.println("Most Common Element after "+k+" is "+retVal);
			
	int[] arr2={2,3,2,4,2,2,3,2,1,2,2,2};
	k=2;
	printArraySummary(arr2, "The input array");
	retVal=hp.hashMapMostFreqAfterKey(arr2,k);
	System.out.println("Most Common Element after "+k+" is "+retVal);
		
			
	}catch (Exception exception) {
	System.out.print("Exception: "+ exception);
	exception.printStackTrace();
	}
				
}

public static void printArraySummary(int[] intArray, String label) throws Exception {
   	// Case 1: The input Array is null !!
	if (intArray == null) { System.out.println("\n\n Input Array was null !! \n"); return; }
	// Case 2: Print input Array by index (first to last)
	System.out.println();
	System.out.println("************************************************************************");
	System.out.print(label+" : ");
	int arrayIndex=0;
	for (arrayIndex=0; arrayIndex< intArray.length; arrayIndex++) {
			System.out.print(intArray[arrayIndex]);
			if (arrayIndex< intArray.length-1) {System.out.print(",");}
	} 
	System.out.println();
	System.out.println("*************************************************************************");
	System.out.println();
	Thread.sleep(2000);
	return;
}

}