add 2 leetcode solutions

content/SoftwareEngineering/Leetcode/0001 - Contains Duplicated.md

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+https://leetcode.com/problems/contains-duplicate/description/
+
+#leetcode
+#interview 
+
+Given an integer array `nums`, return `true` if any value appears **at least twice** in the array, and return `false` if every element is distinct.
+
+**Example 1:**
+
+**Input:** nums = [1,2,3,1]
+
+**Output:** true
+
+**Explanation:**
+
+The element 1 occurs at the indices 0 and 3.
+
+**Example 2:**
+
+**Input:** nums = [1,2,3,4]
+
+**Output:** false
+
+**Explanation:**
+
+All elements are distinct.
+
+**Example 3:**
+
+**Input:** nums = [1,1,1,3,3,4,3,2,4,2]
+
+**Output:** true
+
+**Constraints:**
+
+- `1 <= nums.length <= 105`
+- `-109 <= nums[i] <= 109`
+  
+
+Here's how you can solve the problem using Python. You can leverage the properties of sets to check for duplicates efficiently:
+
+```python
+class Solution:
+    def containsDuplicate(self, nums: List[int]) -> bool:
+        # Create an empty set to store unique elements
+        seen = set()
+        
+        # Iterate through each number in the input list
+        for num in nums:
+            # If the number is already in the set, it means it's a duplicate
+            if num in seen:
+                return True
+            # Otherwise, add the number to the set
+            seen.add(num)
+        
+        # If no duplicates were found, return False
+        return False
+```
+
+### Explanation:
+1. **Initialize a set**: `seen = set()`. Sets in Python do not allow duplicate values, which makes them useful for checking whether an element has already been seen.
+2. **Iterate through `nums`**: For each number in the input list `nums`, check if it already exists in the `seen` set.
+3. **Check for duplicates**:
+   - If `num` is already in `seen`, it means we've encountered a duplicate, so return `True`.
+   - If not, add `num` to the `seen` set.
+4. If we iterate through the entire list without finding a duplicate, return `False`.
+
+### Time Complexity:
+- The time complexity is O(n), where n is the number of elements in the list. Checking and inserting into a set both have an average time complexity of O(1).
+
+### Space Complexity:
+- The space complexity is O(n) because, in the worst case, we might need to store all elements of the input list in the set.
+
+This solution efficiently checks for duplicates using sets and is well-suited for the given constraints.

content/SoftwareEngineering/Leetcode/0002 - Valid Anagram.md

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+
+[242. Valid Anagram](https://leetcode.com/problems/valid-anagram/)
+
+Solved
+
+Easy
+
+Topics
+
+Companies
+
+Given two strings `s` and `t`, return `true` if `t` is an 
+
+anagram
+
+ of `s`, and `false` otherwise.
+
+**Example 1:**
+
+**Input:** s = "anagram", t = "nagaram"
+
+**Output:** true
+
+**Example 2:**
+
+**Input:** s = "rat", t = "car"
+
+**Output:** false
+
+**Constraints:**
+
+- `1 <= s.length, t.length <= 5 * 104`
+- `s` and `t` consist of lowercase English letters.
+
+**Follow up:** What if the inputs contain Unicode characters? How would you adapt your solution to such a case?
+
+
+
+
+
+Here's how you can solve the problem using Python by leveraging sorting or a frequency count approach:
+
+### Approach 1: Sorting
+If two strings are anagrams, they should contain the same characters with the same frequency. By sorting the strings and comparing them, we can check if they are anagrams.
+
+```python
+class Solution:
+    def isAnagram(self, s: str, t: str) -> bool:
+        # If the lengths of s and t are different, they can't be anagrams
+        if len(s) != len(t):
+            return False
+        
+        # Sort both strings and compare
+        return sorted(s) == sorted(t)
+```
+
+### Explanation:
+1. **Check length**: If the lengths of `s` and `t` are different, return `False` immediately because they can't be anagrams.
+2. **Sort and compare**: Sort both strings and check if they are equal. If they are, then `t` is an anagram of `s`.
+
+### Time Complexity:
+- Sorting both strings takes O(n log n) time, where n is the length of the strings.
+
+### Space Complexity:
+- Sorting requires additional space, but it depends on the language implementation. In general, the space complexity is O(1) if the sort is done in place, or O(n) if it creates a new sorted array.
+
+---
+
+### Approach 2: Frequency Count
+Instead of sorting, we can count the frequency of each character in both strings and compare the counts.
+
+```python
+from collections import Counter
+
+class Solution:
+    def isAnagram(self, s: str, t: str) -> bool:
+        # If the lengths of s and t are different, they can't be anagrams
+        if len(s) != len(t):
+            return False
+        
+        # Count the frequency of characters in both strings and compare
+        return Counter(s) == Counter(t)
+```
+
+### Explanation:
+1. **Check length**: If the lengths of `s` and `t` are different, return `False` immediately because they can't be anagrams.
+2. **Frequency count**: Use the `Counter` from the `collections` module to count the frequency of each character in `s` and `t`.
+3. **Compare counts**: If the two `Counter` objects are equal, `t` is an anagram of `s`.
+
+### Time Complexity:
+- Counting the frequency of each character takes O(n) time.
+
+### Space Complexity:
+- The space complexity is O(1) if the character set is fixed (e.g., 26 lowercase English letters), or O(n) if the character set can grow.
+
+### Follow-Up for Unicode Characters:
+If the inputs contain Unicode characters, the same approach will work. The only change would be handling Unicode strings properly, which Python natively supports with its `str` and `Counter` functionalities. So, no modifications are required for the above code to work with Unicode characters.
+
+
+
+ Here's the solution using a hashmap (dictionary) approach to check if two strings are anagrams:
+
+```python
+class Solution:
+    def isAnagram(self, s: str, t: str) -> bool:
+        # If the lengths of s and t are different, they can't be anagrams
+        if len(s) != len(t):
+            return False
+        
+        # Create a dictionary to count characters in s
+        count_s = {}
+        
+        # Count the frequency of each character in s
+        for char in s:
+            if char in count_s:
+                count_s[char] += 1
+            else:
+                count_s[char] = 1
+                
+        # Subtract the frequency of each character in t
+        for char in t:
+            if char in count_s:
+                count_s[char] -= 1
+            else:
+                # If a character in t is not in s, return False
+                return False
+        
+        # If all values in count_s are zero, it's an anagram
+        for count in count_s.values():
+            if count != 0:
+                return False
+                
+        return True
+```
+
+### Explanation:
+1. **Length check**: If `s` and `t` have different lengths, return `False` immediately.
+2. **Count frequency for `s`**: Create a hashmap (`count_s`) where keys are characters in `s` and values are the frequency of each character.
+3. **Adjust frequency for `t`**: For each character in `t`, decrease its count in `count_s`.
+   - If a character in `t` is not in `count_s`, return `False` (since it means `t` has a character not present in `s`).
+4. **Check if all counts are zero**: After processing both strings, all the values in `count_s` should be zero. If not, it means the strings are not anagrams.
+
+### Time Complexity:
+- O(n), where n is the length of the strings. Each character is processed twice (once for counting and once for adjusting).
+
+### Space Complexity:
+- O(1), assuming a fixed character set like lowercase English letters (26 characters). If we consider all Unicode characters, it would be O(n) due to the possible large number of keys in the hashmap.
+
+### Why Use a Hashmap?
+Using a hashmap (dictionary) is efficient for counting elements, as accessing and modifying dictionary entries is O(1). This approach avoids the overhead of sorting and works well even for larger inputs.
+
+Let me know if you'd like to see further optimizations or variations!
+
+
+
+Also good solution
+
+
+```python
+
+class Solution:
+    def isAnagram(self, s: str, t: str) -> bool:
+        if len(s) != len(t):
+            return False
+
+        countS, countT = {}, {}
+
+        for i in range(len(s)):
+            countS[s[i]] = 1 + countS.get(s[i], 0)
+            countT[t[i]] = 1 + countT.get(t[i], 0)
+        return countS == countT
+
+    
+    # easier solution
+    #return True if sorted(s) == sorted(t) else False
+```
+
+