Missing Number Problem & Solution

Given an array nums containing n distinct numbers in the range [0, n], return the only number in the range that is missing from the array.

See the missing number problem on LeetCode.

C++ Solution

The runtime complexity of this algorithm is $O(n)$.

#pragma GCC optimize("Ofast")
#pragma GCC optimization("unroll-loops")

static const int _=[](){std::ios::sync_with_stdio(false);cin.tie(nullptr);cout.tie(nullptr);return 0;}();

class Solution {
  int missingNumber(vector<int>& nums) {
    int sum = nums.size();
    for (int i = 0; i < nums.size(); ++i) {
      sum += i;
      sum -= nums[i];

    return sum;

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