done

problem1.py

@@ -0,0 +1,25 @@
+"""
+We check for every index (nums[i] + 1) if the element present at that index is negative,
+if its negative, mark it as negative i.e. it is present, and in the second pass, return all elements that remain positive
+time is o(n) and space is o(1)
+"""
+
+class Solution(object):
+    def findDisappearedNumbers(self, nums):
+        """
+        :type nums: List[int]
+        :rtype: List[int]
+        """
+        res = []
+        n = len(nums)
+        for i in range(n):
+            index = abs(nums[i]) - 1 #to traverse through the array at each index and
+            if nums[index] > 0: #check if number is not negative, make it negative
+                nums[index] *= -1
+
+        for i in range(n): #second pass, check if any elem is positive, return that index + 1 as missing number
+            if nums[i] > 0:
+                res.append(i+1)
+        return res
+
+

problem2.py

@@ -0,0 +1,42 @@
+"""
+We use the coundary conditions to moodify the pointers and apply the games of rule accordingly, usee the temporary state change method to analyse the board
+then count the changes that were made through counting the number of variations we see (2 and 3 for dead and resurrected accordingly)
+TC is O(m*n) and SC is o(n)
+"""
+
+
+class Solution(object):
+    def gameOfLife(self, board):
+        """
+        :type board: List[List[int]]
+        :rtype: None Do not return anything, modify board in-place instead.
+        """
+        m = len(board)
+        n = len(board[0])
+        dirs = [(-1,-1), (-1,0), (-1,1), (0,-1), (0,1), (1,-1), (1,0), (1,1)]
+        def countAlive(i, j):
+            count = 0
+            for dr, dc in dirs:
+                nr, nc = i + dr, j + dc
+                if nr >= 0 and nc >= 0 and nr < m and nc < n:
+                    if board[nr][nc] == 1 or board[nr][nc] == 2: #2 for originally alive, but marked to die later on
+                        count += 1
+            return count
+
+        for i in range(m):
+            for j in range(n):
+                count = countAlive(i,j)
+                if board[i][j] == 1 and (count > 3 or count < 2):
+                    board[i][j] = 2
+                if board[i][j] == 0 and count == 3:
+                    board[i][j] = 3
+
+        for i in range(m):
+            for j in range(n):
+                if board[i][j] == 3:
+                    board[i][j] = 1
+                if board[i][j] == 2:
+                    board[i][j] = 0
+
+
+