The challenge
You will be given a number and you will need to return it as a string in Expanded Form.
Examples:
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Challenge.expandedForm(12); // Should return "10 + 2"
Challenge.expandedForm(42); // Should return "40 + 2"
Challenge.expandedForm(70304); // Should return "70000 + 300 + 4"
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NOTE: All numbers will be whole numbers greater than 0.
The solution in Java code
Option 1:
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public class Challenge {
public static String expandedForm(int num) {
StringBuffer res = new StringBuffer();
int d = 1;
while(num > 0) {
int nextDigit = num % 10;
num /= 10;
if (nextDigit > 0) {
res.insert(0, d * nextDigit);
res.insert(0, " + ");
}
d *= 10;
}
return res.substring(3).toString();
}
}
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Option 2:
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import java.util.LinkedList;
public class Challenge {
public static String expandedForm(int num) {
LinkedList<String> expandedList = new LinkedList<>();
int digit;
int multiplier = 1;
while (num > 0) {
digit = (num % 10) * multiplier;
if (digit != 0) expandedList.push(Integer.toString(digit));
num /= 10;
multiplier *= 10;
}
return String.join(" + ", expandedList);
}
}
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Option 3:
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import java.util.stream.IntStream;
import static java.util.stream.Collectors.joining;
public class Challenge {
public static String expandedForm(int num) {
var ns = ""+num;
return IntStream.range(0, ns.length())
.mapToObj(i -> ns.charAt(i) + "0".repeat(ns.length() - 1 - i))
.filter(e -> !e.matches("0+"))
.collect(joining(" + "));
}
}
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Test cases to validate our solution
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import org.junit.Test;
import static org.junit.Assert.assertEquals;
import org.junit.runners.JUnit4;
public class SolutionTest {
@Test
public void testSomething() {
assertEquals("10 + 2", Challenge.expandedForm(12));
assertEquals("40 + 2", Challenge.expandedForm(42));
assertEquals("70000 + 300 + 4", Challenge.expandedForm(70304));
}
}
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