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FindMissingNum.java
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FindMissingNum.java
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package array;
import java.util.HashSet;
/**
* In an array 1-100 numbers are stored, one number is missing how do you find it?
*
* @author Tzipora Ziegler
*/
public class FindMissingNum {
/**
* This method stores the numbers 1-100 in a HashSet. It then loops
* through the array of numbers and removes each number from the set.
* At the end of the loop, the number remaining in the set will be the
* number missing from the array.
*
* @param numbers An array of 1-100 numbers with one number missing
* @return The missing number
*/
public int missingNumRemove(int[] numbers) {
// populate set of 1-100
final HashSet<Integer> numberSet = new HashSet<Integer>();
for (int i = 1; i <= 100; i++) {
numberSet.add(i);
}
// loop through the array of number, and remove all existing
for (final int num : numbers) {
numberSet.remove(num);
}
// should be left with the 1 missing number
return numberSet.iterator().next();
}
/**
* This method adds up the numbers 1-100 to compute the expected total.
* It then adds up the numbers found in the array. Finally, it subtracts
* the total found in the array, from the expected total, to determine
* the missing number.
*
* @param numbers An array of 1-100 numbers with one number missing
* @return The missing number
*/
public int missingNumAdd(int[] numbers) {
int expectedTotal = 100;
int total = 0;
for (int i = 1; i < 100; i++) {
expectedTotal += i;
total += numbers[i - 1];
}
return expectedTotal - total;
}
}