[i-mprovising] Week 02 solutions

climbing-stairs/i-mprovising.py

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+"""
+Time complexity O(n)
+Space complexity O(n)
+
+Dynamic programming
+"""
+
+class Solution:
+    def climbStairs(self, n: int) -> int:
+        dp = [0, 1, 2] # distinct ways to reach i steps
+        if n <= 2:
+            return dp[n]
+
+        for i in range(3, n+1):
+            dp.append(dp[i-1] + dp[i-2])
+        return dp[n]

product-of-array-except-self/i-mprovising.py

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+"""
+Time complexity O(n)
+Space complexity O(n)
+
+Prefix sum 
+"""
+
+class Solution:
+    def productExceptSelf(self, nums: List[int]) -> List[int]:
+        products = [1]
+        reverse_products = [1]
+
+        tmp = 1
+        for n in nums[:-1]:
+            tmp *= n
+            products.append(tmp)
+        tmp = 1
+        for n in nums[::-1][:-1]:
+            tmp *= n
+            reverse_products.append(tmp)
+
+        answer = [
+            products[i] * reverse_products[-i-1]
+            for i in range(len(nums))
+        ]
+        return answer

valid-anagram/i-mprovising.py

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+"""
+Time complexity O(n)
+Space complexity O(n)
+"""
+from collections import defaultdict
+
+class Solution:
+    def isAnagram(self, s: str, t: str) -> bool:
+        s_cnt = defaultdict(int)
+        t_cnt = defaultdict(int)
+        for char in s:
+            s_cnt[char] += 1
+        for char in t:
+            t_cnt[char] += 1
+        if s_cnt != t_cnt:
+            return False
+        return True