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  1. Prepare
  2. Tutorials
  3. 10 Days of Statistics
  4. Day 0: Mean, Median, and Mode
  5. Discussions

Day 0: Mean, Median, and Mode

  • RodneyShag
     + 5 comments

    Java solution - passes 100% of test cases

    import java.util.Scanner;
import java.util.Arrays;
import java.util.HashMap;

// Time Complexity: O(n log n) due to sorting
public class Solution {
    public static void main(String[] args) {
        /* Save input */
        Scanner scan = new Scanner(System.in);
        int size = scan.nextInt();
        int [] array = new int[size];
        for (int i = 0; i < size; i++) {
            array[i] = scan.nextInt();
        }
        scan.close();
        
        /* Sort array: O(n log n) runtime */
        Arrays.sort(array);
        
        /* Calculate Mean */
        int total = 0;
        for (int num : array) {
            total += num;
        }
        double mean = (double) total / size;
        
        /* Calculate Median */
        double median;
        if (size % 2 == 0) {
            median = (array[size / 2 - 1] + array[size / 2]) / 2.0;
        } else {
            median = array[size / 2];
        }
        
        /* Calculate Mode - if there's a tie, choose the smaller number */
        HashMap<Integer, Integer> map = new HashMap<>();
        int maxOccurrences = 0;
        int mode = Integer.MAX_VALUE;
        for (int num : array) {
            map.merge(num, 1, Integer::sum);
            int occurrences = map.get(num);
            if (occurrences > maxOccurrences || (occurrences == maxOccurrences && num < mode)) {
                maxOccurrences = occurrences;
                mode = num;
            }
        }

        /* Print results */
        System.out.println(mean);
        System.out.println(median);
        System.out.println(mode);
    }
}

    From my HackerRank Java solutions

    • PraveenaT
       + 3 comments

      i m unable to pass test case 3, can anyone help me?

      • RodneyShag
         + 0 comments

        Hi. Try posting your code in a new thread to reach a wider audience and for us to have the ability to see what's wrong. HackerRank solutions.

      • saikishore_namb1
         + 1 comment

        my code is also not able to pass test case 3,please help

        • RodneyShag
           + 0 comments

          Hi. Try posting your code in a new thread to reach a wider audience and for us to have the ability to see what's wrong. You can tag me in the post and I will take a look also.

          HackerRank solutions.

      • chaitanya_G
         + 1 comment

        hi buddy here is the one of the easy code for you:

        import java.io.; import java.util.;

        public class Solution {

        public static void main(String[] args) {

        /*Take input from user*/
Scanner sc = new Scanner(System.in);

int n =0;
n = sc.nextInt();

int arr[] = new int[n];

//////////////mean code starts here//////////////////
int sum = 0;
for(int i=0;i<n; i++)
{
     arr[i] = sc.nextInt();
     sum += arr[i]; 
}
System.out.println((double)sum/n); 
//////////////mean code ends here//////////////////


//////////////median code starts here//////////////////
Arrays.sort(arr);
int val = arr.length/2;
System.out.println((arr[val]+arr[val-1])/2.0); 
//////////////median code ends here//////////////////


//////////////mode code starts here//////////////////
int maxValue=0;
int maxCount=0;

for(int i=0; i<n; ++i)
{
    int count=0;

    for(int j=0; j<n; ++j)
    {
        if(arr[j] == arr[i])
        {
            ++count;
        }

        if(count > maxCount)
        {
            maxCount = count;
            maxValue = arr[i];
        }
    }
} 
System.out.println(maxValue);

        //////////////mode code ends here//////////////////

        }

        }

        • jeff_g_du
           + 0 comments
              // check mode, not necessary to use HashMap 
            // or double for loops to calculate counts for each item;
    // assuming the first item would be the mode
            int mode = arr[0];
    int max = 1;
    int appearance = 1;        

    for(int i=1; i<arr.length; i++){

        if ( arr[i] == arr[i-1] ) {
            appearance ++; 

        } else {
            appearance = 1; 
        }

        if( appearance > max ){
            max = appearance; 
            mode = arr[i]; 
        }

    }

    • Passiq
       + 1 comment

      what is the use of map.merge(num,1,Integer::sum); can you help me please

      • RodneyShag
         + 1 comment

        That's a function that's part of HashMap, as shown here. If num does not exist as a key, it puts num as key, and 1 as a value into the HashMap.

        If on the other hand num already exists, then it just increments the value of num by 1.

        HackerRank solutions.

        • [deleted]           + 2 comments

          other than hashmap there isnt any other code for mode calculation?

          • RodneyShag
             + 0 comments

            If the numbers are within a certain range, like 1 to 10, you can use a 10-element array.

            HackerRank solutions.

          • nabiljdaoud
             + 0 comments

            Yeah, I took advantage of the fact that I sorted the array to find the median.

            ` import java.util.Arrays;

            Arrays.sort(X); // X is our array of integers

                int mode = -1;
    int last = -1;
    int maxFreq = 0;
    int freq = 1;
    for (int x : X) {
        if (x == last) {
            freq++;
        } else {
            freq = 1;
        }

        // because numbers are sorted I only have to worry about strictly greater than.
        if (freq > maxFreq) { 
            maxFreq = freq;
            mode = x;
        }

        last = x;
    }

    • bahuguna_akshay
       + 0 comments

      Bro @rshaghoulian my Java solution does not run Test case 3 rest its working fine. As test data set is too huge i am not able to find the problem.

      Can you please review my code and tell me the possible error? Thanks in advance !

      import java.io.; import java.util.;

      public class Solution {

      public static void main(String[] args) {
    /* Enter your code here. Read input from STDIN. Print output to STDOUT. Your class should be named Solution. */
    Scanner sc = new Scanner(System.in);
    int n = sc.nextInt();
    int []arr = new int[n];
    for(int i=0;i<n;i++){
        arr[i]=sc.nextInt();
    }
    sc.close();
    Arrays.sort(arr);

    //mean
    float sum=0;
    for(int i=0;i<n;i++){
        sum = sum + arr[i];
    }
    System.out.printf("%.1f",sum/n); System.out.println();

    //median
    int l=arr.length;
    if(l%2==1) {
        float med=arr[l/2];
        System.out.printf("%.1f",med);
    }else {
        int a=l/2;
        int b=a-1;
        double medd = (double)(arr[a]+arr[b])/2;
        System.out.printf("%.1f",medd);
    }
     System.out.println();

     //mode
    int mode=arr[0],max=0,count=0;
    HashMap<Integer, Integer> map = new HashMap<>();

    for(int i=0;i<l-1;i++) {
        if(arr[i]==arr[i+1]) {
            count++;
            map.put(arr[i], count);
        }
        else {
            count=0;
        }
    }
    if(map.isEmpty())System.out.println(mode);
    else{
    for (int i : map.keySet()) {
        if(map.get(i)>max) {
            max=map.get(i);
            mode=i;
        }
    }
    System.out.println(mode);
    }

}

      }

    • crystal_hansen
       + 0 comments

      Thank YOU! I couldnt get the third test with mode to work till i used your hashmap! :) you rock

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