[daehyun99] WEEK 03 Solutions (#2738)

* Solve: isPalindrome

* Solve: hammingWeight

* Solve: combinationSum

* Solve: numDecodings

* Solve: maxSubArray

Author: daehyun99

combination-sum/daehyun99.py

@@ -0,0 +1,20 @@
+from collections import deque
+class Solution:
+    def combinationSum(self, candidates: List[int], target: int) -> List[List[int]]:
+        result = []
+        candidates = sorted(candidates)
+        que = deque([candidate] for candidate in candidates)
+        while len(que) > 0:
+            values = que.popleft()
+            sum_values = sum(values)
+            if sum_values == target:
+                result.append(values)
+                continue
+            for candidate in candidates:
+                if values[-1] > candidate:
+                    continue
+                if sum_values + candidate <= target:
+                    temp = values.copy()
+                    temp.append(candidate)
+                    que.append(temp)
+        return result

decode-ways/daehyun99.py

@@ -0,0 +1,25 @@
+from collections import deque
+class Solution:
+    def numDecodings(self, s: str) -> int:
+        decoded = set([str(i) for i in range(1, 27)])
+        counts = [0 for i in range(len(s))]
+        if len(s) == 1:
+            if s == "0":
+                return 0
+            else:
+                return 1
+        
+        if s[0] in decoded:
+            counts[0] += 1
+        if s[1] in decoded:
+            counts[1] += counts[0]
+        if s[0:2] in decoded:
+            counts[1] += 1
+
+        for i in range(2, len(s)):
+            if s[i] in decoded:
+                counts[i] += counts[i-1]
+            if s[i-1:i+1] in decoded:
+                counts[i] += counts[i-2]
+        return counts[-1]
+

maximum-subarray/daehyun99.py

@@ -0,0 +1,20 @@
+class Solution:
+    def maxSubArray(self, nums: List[int]) -> int:
+        if max(nums) <= 0:
+            return max(nums)
+
+        result = max(nums)
+        val = 0
+        for i in range(len(nums)-1, -1, -1):
+            val += nums[i]
+            if val < 0:
+                val = 0
+            result = max(result, val)
+
+        val = 0
+        for i in range(len(nums)):
+            val += nums[i]
+            if val < 0:
+                val = 0
+            result = max(result, val)
+        return result

number-of-1-bits/daehyun99.py

@@ -0,0 +1,3 @@
+class Solution:
+    def hammingWeight(self, n: int) -> int:
+        return n.bit_count()

valid-palindrome/daehyun99.py

@@ -0,0 +1,12 @@
+class Solution:
+    def isPalindrome(self, s: str) -> bool:
+        forward = ""
+
+        s = s.lower()
+
+        for string in s:
+            if 97 <= ord(string) <= 122 or 48 <= ord(string) <= 57:
+                forward += string
+        backward = forward[::-1]
+
+        return True if forward == backward else False