added problem67

Author: dampdigits

problem67/README.md

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+# 338. Counting Bits
+
+Given an integer n, return an array ans of length n + 1 such that for each i (0 <= i <= n), ans[i] is the number of 1's in the binary representation of i.
+
+
+## Example 1:
+
+Input: n = 2
+Output: [0,1,1]
+Explanation:
+0 --> 0
+1 --> 1
+2 --> 10
+
+## Example 2:
+
+Input: n = 5
+Output: [0,1,1,2,1,2]
+Explanation:
+0 --> 0
+1 --> 1
+2 --> 10
+3 --> 11
+4 --> 100
+5 --> 101
+ 
+
+## Constraints:
+
+0 <= n <= 105
+ 
+
+## Follow up:
+
+It is very easy to come up with a solution with a runtime of O(n log n). Can you do it in linear time O(n) and possibly in a single pass?
+Can you do it without using any built-in function (i.e., like __builtin_popcount in C++)?