Missing Number

Given an array containing n distinct numbers taken from 0, 1, 2, ..., n, find the one that is missing from the array.

For example, Given nums = [0, 1, 3] return 2.

Note: Your algorithm should run in linear runtime complexity. Could you implement it using only constant extra space complexity?

Credits:Special thanks to @jianchao.li.fighter for adding this problem and creating all test cases.

Solution

public class Solution {
    public int missingNumber(int[] nums) {
        if (nums == null || nums.length == 0) return -1;

        for (int i = 0; i < nums.length; i++) {
            while (nums[i] < nums.length && nums[i] != i) {
                swap(nums, i, nums[i]);
            }
        }

        for(int i = 0; i < nums.length; i ++) {
            if (i != nums[i]) {
                return i;
            }
        }

        return nums.length;
    }

    private void swap(int[] nums, int i, int j) {
        int temp = nums[i];
        nums[i] = nums[j];
        nums[j] = temp;
    }
}