:squirrel:

Author: angelgladin

3sum.py

@@ -0,0 +1,28 @@
+# 15. 3Sum
+# https://leetcode.com/problems/3sum/
+
+class Solution:
+    def threeSum(self, nums: List[int]) -> List[List[int]]:
+        nums.sort()
+        n = len(nums)
+        ans = []
+        for i in range(n-2):
+            if i > 0 and nums[i] == nums[i-1]:
+                continue
+            j = i+1
+            k = n-1
+            while j < k:
+                s = nums[i] + nums[j] + nums[k]
+                if s == 0:
+                    ans.append([nums[i], nums[j], nums[k]])
+                    while j < k and nums[j] == nums[j+1]:
+                        j += 1
+                    while j < k and nums[k] == nums[k-1]:
+                        k -= 1
+                    j += 1
+                    k -= 1
+                elif s > 0:
+                    k -= 1
+                else:
+                    j += 1
+        return ans

accounts-merge.py

@@ -0,0 +1,37 @@
+# 721. Accounts Merge
+# https://leetcode.com/problems/accounts-merge/
+
+from collections import defaultdict
+class Solution:
+    def accountsMerge(self, accounts: List[List[str]]) -> List[List[str]]:
+        def dfs(stack, emails, explored, graph):
+            while stack:
+                u = stack.pop()
+                emails.append(u)
+                for v in graph[u]:
+                    if v not in explored:
+                        explored.add(v)
+                        stack.append(v)
+        
+        graph = defaultdict(set)
+        email_to_name = dict()
+        for account in accounts:
+            name = account[0]
+            for i in range(1, len(account)):
+                email_to_name[account[i]] = name
+                if i == 1:
+                    continue
+                graph[account[i]].add(account[i-1])
+                graph[account[i-1]].add(account[i])
+
+        explored = set()
+        ans = []
+        for email in email_to_name.keys():
+            if email not in explored:
+                explored.add(email)
+                stack = [email]
+                emails = []
+                dfs(stack, emails, explored, graph)
+                emails.sort()
+                ans.append([email_to_name[email]] + emails)
+        return ans

add-binary.py

@@ -1,3 +1,4 @@
+# 67. Add Binary
 # https://leetcode.com/problems/add-binary/
 
 class Solution:

add-two-numbers.py

@@ -1,3 +1,4 @@
+# 2. Add Two Numbers
 # https://leetcode.com/problems/add-two-numbers/
 
 # Definition for singly-linked list.

alien-dictionary.py

@@ -1,3 +1,6 @@
+# 269. Alien Dictionary
+# https://leetcode.com/problems/alien-dictionary/
+
 class Solution:
     def alienOrder(self, words: List[str]) -> str:
         from collections import defaultdict

backspace-string-compare.py

@@ -1,3 +1,4 @@
+# 844. Backspace String Compare
 # https://leetcode.com/problems/backspace-string-compare/
 
 class Solution:

binary-search-tree-iterator.py

@@ -1,3 +1,4 @@
+# 173. Binary Search Tree Iterators
 # https://leetcode.com/problems/binary-search-tree-iterator/
 
 # Definition for a binary tree node.

combination-sum-ii.py

@@ -1,3 +1,4 @@
+# 40. Combination Sum II
 # https://leetcode.com/problems/combination-sum-ii/
 
 class Solution:

combination-sum.py

@@ -0,0 +1,18 @@
+# 39. Combination Sum
+# https://leetcode.com/problems/combination-sum/
+
+class Solution:
+    def combinationSum(self, candidates: List[int], target: int) -> List[List[int]]:
+        def backtrack(l, k, s, idx, n, aux, ans):
+            if s == k:
+                ans.append(aux[:])
+            elif s > k:
+                return
+            for i in range(idx, n):
+                aux.append(l[i])
+                backtrack(l, k, s+l[i], i, n, aux, ans)
+                aux.pop()
+        
+        ans = []
+        backtrack(candidates, target, 0, 0, len(candidates), [], ans)
+        return ans

confusing-number.py

@@ -1,3 +1,4 @@
+# 1056. Confusing Number
 # https://leetcode.com/problems/confusing-number/
 
 class Solution: