Docs: add description for solved questions

Author: HC-kang

contains-duplicate/HC-kang.ts

@@ -14,6 +14,8 @@ Input: nums = [1,1,1,3,3,4,3,2,4,2]
 Output: true
  */
 
+// Time complexity: O(n)
+// Space complexity: O(n)
 function containsDuplicate(nums: number[]): boolean {
   return nums.length !== new Set(nums).size;
 }

number-of-1-bits/HC-kang.ts

@@ -21,12 +21,17 @@ The input binary string 1111111111111111111111111111101 has a total of thirty se
  */
 
 function hammingWeight(n: number): number {
+  // Time complexity: O(logn)
+  // Space complexity: O(logn)
+  // but it has a better readability
   return n.toString(2).split('1').length - 1;
 
-  // let count = 0;
-  // while (n !== 0) {
-  //   count += n & 1;
-  //   n >>>= 1;
-  // }
-  // return count;
+  // Time complexity: O(logn)
+  // Space complexity: O(1)
+  let count = 0;
+  while (n !== 0) {
+    count += n & 1;
+    n >>>= 1;
+  }
+  return count;
 }