[eunice-hong] Week 03 solutions

number-of-1-bits/eunice-hong.ts

@@ -0,0 +1,7 @@
+function hammingWeight(n: number): number {
+  // 1. convert the number to a binary string
+  const binaryString = n.toString(2);
+
+  // 2. count the number of 1s in the binary string
+  return binaryString.split("").filter((char) => char === "1").length;
+}

valid-palindrome/eunice-hong.ts

@@ -0,0 +1,30 @@
+function isPalindrome(s: string): boolean {
+  // 1. filter out non-alphanumeric characters
+  const validChars =
+    "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnlopqrstuvwxyz0123456789";
+
+  // 2. compare the first and last characters
+  let i = 0;
+  let j = s.length - 1;
+
+  while (i < j) {
+    const head = s[i];
+    const tail = s[j];
+
+    if (!validChars.includes(head)) {
+      // 3. if the characters are not alphanumeric, move the pointer inward
+      i++;
+    } else if (!validChars.includes(tail)) {
+      // 3. if the characters are not alphanumeric, move the pointer inward
+      j--;
+    } else if (head.toLowerCase() !== tail.toLowerCase()) {
+      // 4. if the characters are not the same, return false
+      return false;
+    } else {
+      // 5. if the characters are the same, move the pointers inward
+      i++;
+      j--;
+    }
+  }
+  return true;
+}