[changhyumm] WEEK 02 solutions

3sum/changhyumm.py

@@ -0,0 +1,35 @@
+class Solution:
+    def threeSum(self, nums: List[int]) -> List[List[int]]:
+        # ans = set()
+        # for i in range(len(n)):
+        #     seen = {}
+        #     for j in range(i+1, len(n)):
+        #         complement = -(nums[i] + nums[j])
+        #         if complement in seen:
+        #             ans.add(tuple(sorted([nums[i], nums[j], complement])))
+        #         seen[nums[j]] = j
+        # return [list(triplet) for triplet in ans]
+        # hash + 이중 loop -> O(n^2)
+
+
+        ## 투포인터 활용
+        # sort + loop -> O(nlogn)
+        ans_set = set()
+        nums.sort()
+        for i in range(len(nums)):
+            l = i + 1
+            r = len(nums) - 1
+            while l < r:
+                total = nums[i] + nums[l] + nums[r]
+                if total < 0:
+                    l += 1
+                elif total > 0:
+                    r -= 1
+                else:
+                    # 중복제거
+                    ans_set.add((nums[i], nums[l], nums[r]))
+                    l += 1
+                    r -= 1
+        return list(ans_set)
+
+

climbing-stairs/changhyumm.py

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

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

@@ -0,0 +1,22 @@
+class Solution:
+    def productExceptSelf(self, nums: List[int]) -> List[int]:
+        # ans = [1] * len(nums)
+        # for i in range(len(nums)):
+        #     for j in range(len(nums)):
+        #         if i != j:
+        #             ans[i] = ans[i] * nums[j]
+        # return ans
+        # 시간복잡도를 줄이기 위해서 이중루프를 안쓰는 방법으로
+        left = [1] * len(nums)
+        right = [1] * len(nums)
+        for i in range(len(nums) - 1):
+            left[i+1] = left[i] * nums[i]
+        print(left)
+        for j in range(len(nums) - 1, 0, -1):
+            right[j-1] = right[j] * nums[j]
+        print(right)
+
+        answer = []
+        for k in range(len(left)):
+            answer.append(left[k]*right[k])
+        return answer

valid-anagram/changhyumm.py

@@ -0,0 +1,26 @@
+class Solution:
+    def isAnagram(self, s: str, t: str) -> bool:
+        if len(s) != len(t):
+            return False
+        # sorted_s = sorted(s)
+        # sorted_t = sorted(t)
+        # for i in range(len(s)):
+        #     if sorted_s[i] != sorted_t[i]:
+        #         return False
+        # return True
+        # 시간복잡도가 O(nlog(n))
+
+        # Hashmap 사용하는 방법으로 변경
+        counter = {}
+        for char in s:
+            counter[char] = counter.get(char, 0) + 1
+        for char in t:
+            if char in counter and counter[char] != 0:
+                counter[char] -= 1
+            elif char in counter and counter[char] == 0:
+                return False
+            else:
+                return False
+        # 시간복잡도 O(n)
+        # 공간복잡도 O(n)
+        return True