[HYUNAHKO] WEEK 02 solutions

climbing-stairs/HYUNAHKO.py

@@ -0,0 +1,27 @@
+class Solution:
+    def climbStairs(self, n: int) -> int:
+        if (n<1 or n>45):
+            return 0
+
+        def factorial(num):
+            if num <= 1:
+                return 1
+
+            result = 1 
+            for i in range(2, num+1):
+                result *= i
+            return result 
+
+        steps = 0
+        cur_steps = 1
+        quotient = n // 2
+        k=0
+
+        for _ in range(quotient+1):  
+            cur_steps = factorial(n-k) / (factorial(k)*factorial(n-2*k))  
+            k+=1
+            steps += cur_steps
+
+        return int(steps)
+
+

combination-sum/HYUNAHKO.py

@@ -0,0 +1,24 @@
+class Solution:
+    def combinationSum(self, candidates: List[int], target: int) -> List[List[int]]:
+        result = []
+
+        def backtrack(start_idx, current_combination, current_sum):
+            if current_sum == target:
+                result.append(current_combination[:]) 
+                return
+            if current_sum > target:
+                return
+
+            # 모든 후보 탐색
+            for i in range(start_idx, len(candidates)):
+                # 현재 숫자 선택
+                current_combination.append(candidates[i])
+
+                # 같은 숫자를 다시 사용할 수 있으므로 i부터 시작
+                backtrack(i, current_combination, current_sum + candidates[i])
+
+                # 백트래킹
+                current_combination.pop()
+
+        backtrack(0, [], 0)
+        return result

number-of-1-bits/HYUNAHKO.py

@@ -0,0 +1,9 @@
+class Solution:
+    def hammingWeight(self, n: int) -> int:
+        result = 1
+        while (n//2 != 0):
+            remainder = n % 2
+            if (remainder==1):
+                result+=1
+            n = n//2
+        return result

product-of-array-except-self/HYUNAHKO.py

@@ -0,0 +1,18 @@
+class Solution:
+    def productExceptSelf(self, nums: List[int]) -> List[int]:
+        n = len(nums)
+        result_list = [0] * n
+        if len(nums) <2 or len(nums) > 1e5:
+            return None 
+
+        p = 1
+        for i in range(n):
+            result_list[i] = p
+            p *= nums[i]            
+
+        p = 1
+        for i in range(n - 1, -1, -1): 
+            result_list[i] *= p
+            p *= nums[i] 
+
+        return result_list

valid-anagram/HYUNAHKO.py

@@ -0,0 +1,25 @@
+from collections import Counter
+
+class Solution:
+    def isAnagram(self, s: str, t: str) -> bool:
+        letter_dict1 = {}
+        letter_dict2 = {}
+        letter_list1 = list(s)
+        letter_list2 = list(t)
+
+        for i in letter_list1:
+            letter_dict1[i] = letter_dict1.get(i, 0) + 1
+
+        for j in letter_list2:
+            letter_dict2[j] = letter_dict2.get(j, 0) + 1
+
+        if (letter_dict1 == letter_dict2):
+            return True 
+        else: 
+            return False
+
+
+class Solution:
+    def isAnagram(self, s: str, t: str) -> bool:
+        return Counter(s) == Counter(t)
+

valid-palindrome/HYUNAHKO.py

@@ -0,0 +1,11 @@
+class Solution:
+    def isPalindrome(self, s: str) -> bool:
+        s = s.lower()
+        result = [char for char in s if char.isalnum()]
+
+        n = len(result)
+        for i in range(n):
+            str1 = result[i]
+            if (str1 != result[n-i-1]):
+                return False
+        return True