Code and approach to solve Contains Duplicate problem of leetcode

class Solution:
    def containsDuplicate(self, nums: List[int]) -> bool:
        seen = set()
        for i in nums:
            if i in seen:
                return True
            else :
                seen.add(i)

        return False

PROBLEM

so in the ques we have given an array nums and we have to check if there is any duplicate element in the array or not.

if any element appears more than one time then we have to return True, otherwise we return False.

like here nums = [1,2,3,1], 1 is present two times so it contains a duplicate and the answer will be True.

but if nums = [1,2,3,4], every element is unique so the answer will be False.

APPROACH

so here we use a set to keep track of the elements that we have already seen.

first we create an empty set called seen.

then we loop through every element of nums.

for every element we check if it is already present in seen.

if it is already present, it means that we have seen this element before, so it is a duplicate and we immediately return True.

otherwise we add that element into seen and continue the loop.

if the complete array is checked and we never find a duplicate, then we return False.

for example nums = [1,2,3,1]:

1 -> not in set -> add 1

2 -> not in set -> add 2

3 -> not in set -> add 3

1 -> already in set -> duplicate found -> return True

CODE EXPLAINATION

python
nums = [1,2,3,1]
seen = set()  -> creating an empty set called seen where we will store the elements that we have already seen.

for i in nums:  -> looping through every element of nums one by one.

if i in seen:
    return True  -> checking if the current element i is already present in seen.

if it is already present, it means the same element appeared before, so it is a duplicate and we return True.

else:
    seen.add(i) -> if the current element is not already present in seen, we add it to the set so we can check it against the upcoming elements.

return False    -> if the loop finishes without finding any duplicate element, it means every element is unique, so we return False.