[HodaeSsi] Week 02

3sum/HodaeSsi.py

@@ -0,0 +1,21 @@
+class Solution:
+    def threeSum(self, nums: List[int]) -> List[List[int]]:
+        answerSet = set()
+        nums.sort()
+
+        for i in range(len(nums) - 2):
+            leftIdx = i + 1
+            rightIdx = len(nums) - 1
+            while leftIdx < rightIdx:
+                sum = nums[i] + nums[leftIdx] + nums[rightIdx]
+                if sum < 0:
+                    leftIdx += 1
+                elif sum > 0:
+                    rightIdx -= 1
+                else:
+                    answerSet.add((nums[i], nums[leftIdx], nums[rightIdx]))
+                    leftIdx = leftIdx + 1
+                    rightIdx = rightIdx - 1
+
+        return list(answerSet)
+

climbing-stairs/HodaeSsi.py

@@ -0,0 +1,12 @@
+class Solution:
+    def climbStairs(self, n: int) -> int:
+        dp = []
+        dp.append(0)
+        dp.append(1)
+        dp.append(2)
+
+        for i in range(3, n + 1):
+            dp.append(dp[i - 1] + dp[i - 2])
+
+        return dp[n]
+

construct-binary-tree-from-preorder-and-inorder-traversal/HodaeSsi.py

@@ -0,0 +1,12 @@
+class Solution:
+    def buildTree(self, preorder: List[int], inorder: List[int]) -> Optional[TreeNode]:
+        if inorder == []:
+            return None
+
+        mid = preorder.pop(0)
+        midIdx = inorder.index(mid)
+        left = self.buildTree(preorder, inorder[:midIdx])
+        right = self.buildTree(preorder, inorder[midIdx + 1:])
+
+        return TreeNode(mid, left, right)
+

decode-ways/HodaeSsi.py

@@ -0,0 +1,28 @@
+class Solution:
+    def numDecodings(self, s: str) -> int:
+        dp = []
+        if (s[0] == '0'):
+            return 0
+        dp.append(1)
+
+        for idx, _ in enumerate(s):
+            if idx == 0:
+                continue
+            if s[idx] == '0':
+                if s[idx-1] == '1' or s[idx-1] == '2':
+                    if idx == 1:
+                        dp.append(1)
+                    else:
+                        dp.append(dp[idx-2])
+                else:
+                    return 0
+            elif s[idx-1] == '1' or (s[idx-1] == '2' and (s[idx] >= '1' and s[idx] <= '6')):
+                if idx == 1:
+                    dp.append(2)
+                else:
+                    dp.append(dp[idx-1] + dp[idx-2])
+            else:
+                dp.append(dp[idx-1])
+
+        return dp[-1]
+

valid-anagram/HodaeSsi.py

@@ -0,0 +1,19 @@
+class Solution:
+    def isAnagram(self, s: str, t: str) -> bool:
+        sLetterDict = {}
+        tLetterDict = {}
+
+        for letter in s:
+            sLetterDict[letter] = sLetterDict.get(letter, 0) + 1
+        for letter in t:
+            tLetterDict[letter] = tLetterDict.get(letter, 0) + 1
+
+        if len(sLetterDict) != len(tLetterDict):
+            return False
+
+        for sKey in sLetterDict.keys():
+            if sKey not in tLetterDict or sLetterDict[sKey] != tLetterDict[sKey]:
+                return False
+
+        return True
+