[leetcode]Missing Number

题目描述如下：

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.

想到的解决方法是假设数字是齐全的，利用等差公式计算应有和，减去现有的数字和即可。代码如下：

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

题目链接：https://leetcode.com/problems/missing-number/