**Longest Consecutive Sequence - Amazon Top Interview Questions**

### Problem Statement :

Given an unsorted array of integers nums, find the length of the longest sequence of consecutive elements. Constraints n ≤ 100,000 where n is the length of nums Example 1 Input nums = [100, 4, 200, 1, 3, 2] Output 4 Explanation The longest sequence of consecutive elements is [1, 2, 3, 4]. so we return its length: 4. Example 2 Input nums = [100, 4, 200, 1, 3, 2, 101, 105, 103, 102, 104] Output 6 Explanation The longest sequence of consecutive elements is [100, 101, 102, 103, 104, 105]. so we return its length: 6.

### Solution :

` ````
Solution in C++ :
int solve(vector<int>& nums) {
int res = 0;
unordered_map<int, int> hash;
for (int i : nums) {
hash[i]++;
}
for (int i : nums) {
if (hash[i] == 0) continue;
int cnt = 1;
int next = i + 1;
int pre = i - 1;
while (hash.find(next) != hash.end() && hash[next] > 0) {
cnt++;
hash[next++]--;
}
while (hash.find(pre) != hash.end() && hash[pre] > 0) {
cnt++;
hash[pre--]--;
}
res = max(res, cnt);
}
return res;
}
```

` ````
Solution in Python :
class Solution:
def solve(self, nums):
nums = set(nums)
best = 0
for x in nums:
if x - 1 not in nums:
y = x + 1
while y in nums:
y += 1
best = max(best, y - x)
return best
```

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