# Longest Consecutive Sequence

Given an unsorted array of integers nums, return *the length of the longest consecutive elements sequence.*

You must write an algorithm that runs in O(n) time.

```
function longestConsecutive(nums) {
if (nums == null || nums.length === 0) return 0;
const set = new Set(nums);
let max = 0;
for (let num of set) {
if (set.has(num - 1)) continue; // make sure starting from the beginning of sequence
let currNum = num;
let currMax = 1;
while (set.has(currNum + 1)) {
currNum++;
currMax++;
}
max = Math.max(max, currMax);
}
return max;
}
```

## Related Problems

Given an array of integers nums containing n + 1 integers where each integer is in the range [1, n] inclusive.

There is only **one repeated number** in nums, return *this repeated number*.

You must solve the problem **without** modifying the array nums and uses only constant extra space.

Given an object, return a valid JSON string of that object. You may assume the object only inludes strings, integers, arrays, objects, booleans, and null. The returned string should not include extra spaces. The order of keys should be the same as the order returned by Object.keys().

Please solve it without using the built-in JSON.stringify method.

The Hamming Distance between two integers is the number of positions at which the corresponding bits are different.

Given two integers x and y, return *the ***Hamming distance*** between them*.

You are given an array prices where prices[i] is the price of a given stock on the ith day.

You want to maximize your profit by choosing a **single day** to buy one stock and choosing a **different day in the future** to sell that stock.

Return *the maximum profit you can achieve from this transaction*. If you cannot achieve any profit, return 0.