• Question
• Solution

Question

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?

Solution

Result: Accepted Time: 16 ms

Here should be some explanations.

int missingNumber(int* nums, int numsSize) {
    for(int i =  0; i < numsSize; i++)
        nums[i] <<= 1;
    for(int i = 0; i < numsSize; i++)
        nums[nums[i]>>1] |=  1;
    int ans = numsSize ;
    for(int i = 0; i < numsSize; i++)
    {
         if(!(nums[i]&1))
            ans = i;
        nums[i] >>= 1;
    }
    return ans;
}

Complexity Analytics

• Time Complexity: $O(n)$
• Space Complexity: $O(1)$