--

12_Backtracking/03. Permutations I.py

@@ -1,2 +1,21 @@
 # https://leetcode.com/problems/permutations/
 
+class Solution:
+    def permute(self, nums: List[int]) -> List[List[int]]:
+        nums.sort()
+        res = []
+
+        def dfs(arr, path):
+            if not arr:
+                res.append(path)
+            for i in range(len(arr)):
+                if i > 0 and arr[i] == arr[i-1]:
+                    continue
+                dfs(arr[:i] + arr[i+1:], path + [arr[i]])
+
+        dfs(nums, [])
+        return res
+
+
+# Time: O(N^2)    # as for each element we are making (n-1) traversal again
+# Space: O(N)     # as we are creating n-1 subarrays

12_Backtracking/04. Permutations II.py

@@ -1 +1,20 @@
-# https://leetcode.com/problems/permutations-ii/
+# https://leetcode.com/problems/permutations-ii/
+
+class Solution:
+    def permuteUnique(self, nums: List[int]) -> List[List[int]]:
+        nums.sort()
+        res = []
+
+        def dfs(arr, path):
+            if not arr:
+                res.append(path)
+            for i in range(len(arr)):
+                if i > 0 and arr[i] == arr[i-1]:
+                    continue
+                dfs(arr[:i] + arr[i+1:], path + [arr[i]])
+
+        dfs(nums, [])
+        return res
+
+# Time: O(N^2)    # as for each element we are making (n-1) traversal again
+# Space: O(N)     # as we are creating n-1 subarrays

14_Queue/01. Sliding Window Maximum.py

@@ -23,7 +23,9 @@ def maxSlidingWindow(self, nums, k):
                 res.append(nums[q[0]])  # as q[0] is largest value in that window 
 
         return res
-
+
+# Time: O(N)
+# Space: O(k)    
 
 '''
 Deque (Doubly Ended Queue) in Python is implemented using the module “collections“. 

16_String/04. Basic Calculator II.py

@@ -0,0 +1,42 @@
+# https://leetcode.com/problems/basic-calculator-ii/
+
+class Solution:
+    def calculate(self, s: str) -> int:
+        n = len(s)
+        sign = '+'
+        stack = []
+
+        i = 0
+        while i < n:
+            if s[i].isdigit():
+                num = s[i]
+                i += 1
+                while i < n and s[i].isdigit():
+                    num += s[i]
+                    i += 1
+                i -= 1
+                num = int(num)
+
+                if sign == '+':
+                    stack.append(num)
+                elif sign == '-':
+                    stack.append(-num)
+                elif sign == '*':
+                    newNum = stack.pop() * num
+                    stack.append(newNum)
+                elif sign == '/':
+                    newNum = math.trunc(stack.pop() / num)
+                    # or can use newNum = int(stack.pop() / num)
+                    # for negative numbers // will not work
+                    stack.append(newNum)
+
+            elif s[i] != ' ':
+                sign = s[i]
+            i += 1
+
+        return sum(stack)
+
+
+# Time: O(N)
+# Space: O(N)
+

16_String/05. Basic Calculator I.py

@@ -0,0 +1,32 @@
+# https://leetcode.com/problems/basic-calculator/
+
+class Solution:
+    def calculate(self, s: str) -> int:
+        res, num, sign, stack = 0, 0, 1, []
+
+        for ch in s:
+            if ch.isdigit():
+                num = num*10 + ord(ch) - ord('0') 
+
+            elif ch in ['+', '-']:
+                res += sign * num
+                num = 0
+                sign = 1 if ch == '+' else -1
+
+            elif ch == '(':
+                stack.append(res)
+                stack.append(sign)
+                res = 0
+                sign = 1
+
+            elif ch == ')':
+                res += sign * num
+                res *= stack.pop()
+                res += stack.pop()
+                num = 0
+
+        return res + sign * num
+
+# Time: O(N)
+# Space: O(N)
+