Java 2D Array logic implementation

Question

I got a question today and tried but doesn't found an relevent solution. The question is:

Suppose we have a 2D array containing the name of city and total number of products. The name of city could repeat in the list.

Now what we have to do is

Count the number of product sold in one city and save them in another 2d array having unique city name and total number of products sold.
Print the second city having highest products sold.

A sample list could be for consideration is:

private static String[][] arr = new String[][]{
        {"New Delhi", "5000"},
        {"Chennai", "4300"},
        {"Goa", "2940"},
        {"New Delhi", "2003"},
        {"Kolkata", "8904"},
        {"Kerala", "8972"},
        {"New Delhi", "8922"},
        {"Chennai", "8217"},
        {"New Delhi", "2462"},
        {"Kolkata", "5564"},
        {"Kerala", "9934"},
        {"New Delhi", "100"},
        {"Kolkata", "892"},
        {"Kerala", "9406"},
        {"New Delhi", "2003"},
        {"Chennai", "1049"}
    };

Note: I already tried this question with Map Interface. Only looking for solution with Multidimensional Array

use a map with city as key and products as value, and you just add all the values foreach key together. At last convert that map to an array — Lino
– Lino, Commented Oct 27, 2017 at 13:29
Already given a try to map and was successful in implementing Map. — Chirag
– Chirag, Commented Oct 27, 2017 at 15:31

Danyal Sandeelo · Accepted Answer · 2017-10-27 18:10:23Z

4

Use HashMap where key will be city and value will be the total count

Iterate over the array
If key exists, get the value of key and increment the count with new values
If key doesn't exist, push the value.

Here is the basic idea:

if(dataMap.get(city)==null){
  dataMap.put(city,value);
 }
else{
 dataMap.put(city,value+dataMap.get(city));
}

You can do the same thing with array as well, but you will need to declare a new array where you will be adding count based on the similar city name. The appropriate data structure for this scenario is HashMap

edited Oct 27, 2017 at 18:10

answered Oct 27, 2017 at 13:34

Danyal Sandeelo

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8 Comments

Lino Over a year ago

Java8 version could be a lot smaller: dataMap.compute(city, ( k, v ) -> v == null ? value : v + value);

Malte Hartwig Over a year ago

@Lino use merge to make it even shorter: dataMap.merge(city, value, (oldV, newV) -> oldV + newV);

Lino Over a year ago

@MalteHartwig even better! I forgot about that

Lealo Over a year ago

@Lino I was worried about how you make the hashmap keys (cities) occur only once, when you loop through a list where they occur multiple times. But I realized in the else block that city key overwrites the old city key. It is not a problem.

Lino Over a year ago

@Lealo no i think you understood me wrong, its just not possible to have 2 times the same key in a HashMap

|

Chirag · Accepted Answer · 2017-12-20 12:33:21Z

Finally done that using 2d array and my code is

import java.util.Arrays;

/**
 *
 * @author Chirag
 */
public class Sampleh {

    private static final String[][] $DATA = new String[][]{
        {"New Delhi", "5000"},
        {"Chennai", "4300"},
        {"Goa", "2940"},
        {"New Delhi", "2003"},
        {"Kolkata", "8904"},
        {"Kerala", "8972"},
        {"New Delhi", "8922"},
        {"Chennai", "8217"},
        {"New Delhi", "2462"},
        {"Kolkata", "5564"},
        {"Kerala", "9934"},
        {"New Delhi", "100"},
        {"Kolkata", "892"},
        {"Kerala", "9406"},
        {"New Delhi", "2003"},
        {"Chennai", "1049"}
    };

    private static String[][] $result = new String[50][2];

    private static void action1() {
        outer:
        for (int i = 0; i < $DATA.length; i++) {
            String curCity = $DATA[i][0];
            Integer curProd = Integer.valueOf($DATA[i][1]);
            for (String[] city : $result) {
                if (city[0] == null) {
                    //for this loop
                    continue;
                }
                if (city[0].equals(curCity)) {
                    //for outer loop;
                    continue outer;
                }
            }
            for (int k = i; k < $DATA.length; k++) {
                if ($DATA[k][0].equals(curCity)) {
                    String n = $DATA[k][1];
                    if (n == null) {
                        n = "0";
                    }
                    curProd += Integer.valueOf(n);
                }
            }
            $result[i][0] = curCity;
            $result[i][1] = "" + curProd;
        }
        {
            //this code removes nulls from result array
            String[][] temp; //a temparory 2d array
            int counter = 0; //counts the num of values excluding nulls
            for (String[] res : $result) {
                if (res[0] == null) {
                    continue;
                }
                ++counter;
            }
            temp = new String[counter][2]; //redefine the temporary 2d array with size of values
            counter = 0;
            for (String[] res : $result) {
                if (res[0] == null) {
                    continue;
                }
                temp[counter][0] = res[0];
                temp[counter][1] = res[1];
                counter++;
            }
            $result = temp; //copy all values from temporary array to global result array
        }

        //prints the final array which is not sorted
        for (String[] r : $result) {
            System.out.println("City " + r[0] + " have " + r[1] + " products");
        }
    }

    private static void action2() {
        String[] cities = new String[$result.length];
        int[] products = new int[$result.length];
        int[] prodCopy = new int[$result.length];

        for (int i = 0; i < $result.length; i++) {
            cities[i] = $result[i][0];
            prodCopy[i] = Integer.valueOf($result[i][1]);
            products[i] = Integer.valueOf($result[i][1]);
        }

        Arrays.sort(products);

        for (int i = 0; i < products.length; i++) {
            int counter = -1;
            for (int p : prodCopy) {
                ++counter;
                if (p == products[i]) {
                    break; //breaks the loop to continue to other code without increasing counter
                }
            }
            $result[i][0] = cities[counter];
            $result[i][1] = "" + prodCopy[counter];
        }

        System.out.println("\nprinting full list sorted as counting of product");
        for (String[] k : $result) {
            System.out.println("City: " + k[0] + " have products " + k[1]);
        }

        int loc = $result.length - 2;
        System.out.println();
        System.out.println("Second highest City is '" + $result[loc][0] + "' having products '" + $result[loc][1] + "'");
        System.out.println();
    }

    public static void main(String... $results) {
        action1();
        action2();
    }
}

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