add cpp solution

Author: jinshendan

May-LeetCoding-Challenge/28-Counting-Bits/Counting-Bits.cpp

@@ -0,0 +1,15 @@
+class Solution {
+public:
+    vector<int> countBits(int num) {
+        vector<int> ans(num+1, 0);
+        int m = 1;
+        for (int i = 1; i <= num; i++){
+            if (i == m){
+                ans[i] = 1;
+                m <<= 1;
+            }
+            else ans[i] = ans[i - m/2] + 1;
+        }
+        return ans;
+    }
+};