MissingNumber.java

package array;

/**
 * Created by gouthamvidyapradhan on 04/07/2017.
 * Given an array containing n distinct numbers taken from 0, 1, 2, ..., n, find the one that is missing from the array.
 * <p>
 * For example,
 * Given nums = [0, 1, 3] return 2.
 * <p>
 * Note:
 * Your algorithm should run in linear runtime complexity. Could you implement it using only constant extra space complexity?
 */
public class MissingNumber {

    public static void main(String[] args) throws Exception {
        int[] nums = {0};
        System.out.println(new MissingNumber().missingNumber(nums));
    }

    public int missingNumber(int[] nums) {
        int sum = 0;
        int n = nums.length;
        for (int num : nums) {
            sum += num;
        }
        int arrSum = (((n + 1)) * n) / 2;
        if (arrSum == sum) return 0;
        else return arrSum - sum;
    }
}