[hi-rachel] WEEK 03 solutions

number-of-1-bits/hi-rachel.py

@@ -0,0 +1,26 @@
+# O(log n) time, O(1) space
+# % 나머지, // 몫 
+
+class Solution:
+    def hammingWeight(self, n: int) -> int:
+        cnt = 0
+
+        while n > 0:
+            if (n % 2) == 1:
+                cnt += 1
+            n //= 2
+
+        return cnt
+
+
+# O(log n) time, O(log n) space
+class Solution:
+    def hammingWeight(self, n: int) -> int:
+        return bin(n).count("1")
+
+
+# TS 풀이
+# O(log n) time, O(log n) space
+# function hammingWeight(n: number): number {
+#     return n.toString(2).split('').filter(bit => bit === '1').length;
+# };

valid-palindrome/hi-rachel.py

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+# O(n) time, O(1) space
+# isalnum() -> 문자열이 영어, 한글 혹은 숫자로 되어있으면 참 리턴, 아니면 거짓 리턴.
+
+class Solution:
+    def isPalindrome(self, s: str) -> bool:
+        l = 0
+        r = len(s) - 1
+
+        while l < r:
+            if not s[l].isalnum():
+                l += 1
+            elif not s[r].isalnum():
+                r -= 1
+            elif s[l].lower() == s[r].lower():
+                l += 1
+                r -= 1
+            else:
+                return False
+        return True
+

valid-palindrome/hi-rachel.ts

@@ -0,0 +1,21 @@
+// O(n) time, O(1) space
+
+function isPalindrome(s: string): boolean {
+  let low = 0,
+    high = s.length - 1;
+
+  while (low < high) {
+    while (low < high && !s[low].match(/[0-9a-zA-Z]/)) {
+      low++;
+    }
+    while (low < high && !s[high].match(/[0-9a-zA-Z]/)) {
+      high--;
+    }
+    if (s[low].toLowerCase() !== s[high].toLowerCase()) {
+      return false;
+    }
+    low++;
+    high--;
+  }
+  return true;
+}