leetcode268 Missing Number

268. Missing Number

Total Accepted:
41297 Total Submissions:
104911 Difficulty: Medium
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?

解法一：

class Solution {
public:
int missingNumber(vector<int>& nums) {
int k = 0;
sort(nums.begin(), nums.end());
for (auto i : nums)
{
if (i != k)
return k;
++k;
}
return k;
}
};

解法二：

class Solution {
public:
int missingNumber(vector<int>& nums) {
int k = 0;
int ans = 0;
for (int i : nums) {
ans += k++ - i;
}
return ans + k;
}
};