給定一個 1-100 的整數數組，請找到其中缺少的數字。

import java.util.Arrays;
import java.util.BitSet;

/**
 * Java program to find missing elements in a Integer array containing numbers
 * from 1 to 100.
 *
 */
public class MissingNumberInArray {

	public static void main(String args[]) {

		// one missing number
		printMissingNumber(new int[] { 1, 2, 3, 4, 6 }, 6);

		// two missing number
		printMissingNumber(new int[] { 1, 2, 3, 4, 6, 7, 9, 8, 10 }, 10);

		// three missing number
		printMissingNumber(new int[] { 1, 2, 3, 4, 6, 9, 8 }, 10);

		// four missing number
		printMissingNumber(new int[] { 1, 2, 3, 4, 9, 8 }, 10);

		// Only one missing number in array
		int[] iArray = new int[] { 1, 2, 3, 5 };
		int missing = getMissingNumber(iArray, 5);
		System.out.printf("Missing number in array %s is %d %n", Arrays.toString(iArray), missing);
	}

	/**
	 * A general method to find missing values from an integer array in Java. This
	 * method will work even if array has more than one missing element.
	 */
	private static void printMissingNumber(int[] numbers, int count) {
		int missingCount = count - numbers.length;
		BitSet bitSet = new BitSet(count);

		for (int number : numbers) {
			bitSet.set(number - 1);
		}

		System.out.printf("Missing numbers in integer array %s, with total number %d is %n", Arrays.toString(numbers),
				count);
		int lastMissingIndex = 0;

		for (int i = 0; i < missingCount; i++) {
			lastMissingIndex = bitSet.nextClearBit(lastMissingIndex);
			System.out.println(++lastMissingIndex);
		}

	}

	/**
	 * Java method to find missing number in array of size n containing numbers from
	 * 1 to n only. can be used to find missing elements on integer array of numbers
	 * from 1 to 100 or 1 - 1000
	 */
	private static int getMissingNumber(int[] numbers, int totalCount) {
		int expectedSum = totalCount * ((totalCount + 1) / 2);
		int actualSum = 0;
		for (int i : numbers) {
			actualSum += i;
		}

		return expectedSum - actualSum;
	}

}