268. Missing Number

题目：

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?

链接： http://leetcode.com/problems/missing-number/

3/5/2017

public class Solution {
    public int missingNumber(int[] nums) {
        int sum = 0;
        int length = nums.length;
        for (int i = 0; i < length; i++) {
            sum += nums[i];
        }
        return length * (length + 1) / 2 - sum;
    }
}