updates

Author: wuduhren

README.md

@@ -13,6 +13,7 @@ Please [BUY ME A COFFEE](https://www.buymeacoffee.com/chriswu) if you want to sh
 # Leetcode Problem Lists
 I found it makes sense to solve similar problems together, so that we can recognize the problem faster when we encounter a new one. My suggestion is to skip the HARD problems when you first go through these list.
 
+* https://neetcode.io/practice (150 problems with video explaination)
 * https://www.programcreek.com/2013/08/leetcode-problem-classification/
 * https://github.com/wisdompeak/LeetCode
 * https://docs.google.com/spreadsheets/d/1SbpY-04Cz8EWw3A_LBUmDEXKUMO31DBjfeMoA0dlfIA/edit#gid=126913158 ([huahua](https://www.youtube.com/user/xxfflower/videos)).

problems/python3/missing-number.py

@@ -0,0 +1,12 @@
+class Solution:
+    def missingNumber(self, nums: List[int]) -> int:
+        N = len(nums)
+        ans = 0
+        
+        for n in range(N+1):
+            ans ^= n
+        
+        for n in nums:
+            ans ^= n
+        
+        return ans

problems/python3/reverse-integer.py

@@ -0,0 +1,16 @@
+class Solution:
+    def reverse(self, x: int) -> int:
+        MAX = 2**31-1
+        MIN = -2**31
+        ans = 0
+        
+        while x:
+            digit = int(math.fmod(x, 10))
+            x = int(x/10)
+            
+            if ans>MAX//10 or (ans==MAX//10 and digit>MAX%10): return 0
+            if ans<MIN//10 or (ans==MIN//10 and digit<MIN%10): return 0
+            
+            ans = ans*10 + digit
+            
+        return ans

problems/python3/sum-of-two-integers.py

@@ -0,0 +1,12 @@
+"""
+Does not work with negative values yet.
+"""
+class Solution:
+    def getSum(self, a: int, b: int) -> int:
+        ans = a^b
+        carry = (a&b)<<1
+        
+        while carry!=0:
+            ans, carry = ans^carry, (ans&carry)<<1
+            
+        return ans