Merge branch 'Math' of https://github.com/soapyigu/LeetCode_Swift int…

…o Math

Math/CountingBits.swift

@@ -0,0 +1,28 @@
+/**
+ * Question Link: https://leetcode.com/problems/counting-bits/
+ * Primary idea:
+ *   bits[i] = bits[i - p] + 1, while p is the largest power of two that smaller than i;
+ *
+ *  Time Complexity: O(n), Space Complexity: O(n)
+ */
+
+class CountingBits {
+    func countBits(num: Int) -> [Int] {
+        guard num > 0 else {
+            return [0]
+        }
+
+        var bits = [Int](count: num + 1, repeatedValue: 0)
+        var x = 1
+        for i in 1...num {
+            if i == x {
+                x = x << 1
+                bits[i] = 1
+            } else {
+                bits[i] = bits[i - (x >> 1)] + 1
+            }
+        }
+
+        return bits
+    }
+}

README.md

@@ -170,6 +170,7 @@
 [Excel Sheet Column Number](https://leetcode.com/problems/excel-sheet-column-number/)| [Swift](./Math/ExcelSheetColumnNumber.swift)| Easy| O(n)| O(1)|
 [Roman to Integer](https://leetcode.com/problems/roman-to-integer/)| [Swift](./Math/RomanToInteger.swift)| Easy| O(n)| O(n)|
 [Trapping Rain Water](https://leetcode.com/problems/trapping-rain-water/)| [Swift](./Math/TrappingRainWater.swift)| Hard| O(n)| O(n)|
+[Counting Bits](https://leetcode.com/problems/counting-bits/)| [Swift](./Math/CountingBits.swift)| Medium| O(n)| O(n)|
 
 ## Search
 | Title | Solution | Difficulty | Time | Space |
@@ -308,7 +309,7 @@
 |		|	341	|	[Flatten Nested List Iterator](https://leetcode.com/problems/flatten-nested-list-iterator/)	|	Medium
 |		|	340	|	[Longest Substring with At Most K Distinct Characters](https://leetcode.com/problems/longest-substring-with-at-most-k-distinct-characters/)  ♥	|	Hard
 |	[Swift](./DP/NestedListWeightSum.swift)	|	339	|	[Nested List Weight Sum](https://leetcode.com/problems/nested-list-weight-sum/)  ♥	| Easy
-|		|	338	|	[Counting Bits](https://leetcode.com/problems/counting-bits/)	|	Medium
+|	[Swift](./Math/CountingBits.swift)	|	338	|	[Counting Bits](https://leetcode.com/problems/counting-bits/)	|	Medium
 |		|	337	|	[House Robber III](https://leetcode.com/problems/house-robber-iii/)	|	Medium
 |		|	336	|	[Palindrome Pairs](https://leetcode.com/problems/palindrome-pairs/)	|	Hard
 |		|	335	|	[Self Crossing](https://leetcode.com/problems/self-crossing/)	|	Hard