#Leetcode# 268. Missing Number

https://leetcode.com/problems/missing-number/

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

Example 1:

Input: [3,0,1]
Output: 2

Example 2:

Input: [9,6,4,2,3,5,7,0,1]
Output: 8

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

代码：

class Solution {
public:
    int missingNumber(vector<int>& nums) {
        int n = nums.size();
        int ans = 0;
        for(int i = 0; i < n; i ++)
            ans += (nums[i] - i - 1);
        return abs(ans);
    }
};

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