Solution as on 01-03-2022 09:38 am

Author: knockcat

0338. Counting Bits.cpp

@@ -1,20 +1,48 @@
 338. Counting Bits
 
-class Solution {
+    class Solution
+{
 public:
-    vector<int> countBits(int n) {
+    vector<int> countBits(int n)
+    {
         vector<int> ans;
-        for(int i = 0; i<=n; i++)
+        for (int i = 0; i <= n; i++)
         {
             int sum = 0;
             int num = i;
-            while(num != 0)
+            while (num != 0)
             {
-                sum += num%2;
-                num = num/2;
+                sum += num % 2;
+                num = num / 2;
             }
             ans.push_back(sum);
         }
         return ans;
     }
+};
+
+// Another Approach
+
+class Solution
+{
+public:
+    vector<int> countBits(int n)
+    {
+
+        // n+1 as we are going to count from 0 to n
+        vector<int> t(n + 1);
+
+        // t[0] will be 0 beacuse 0 has count of set bit is 0;
+        t[0] = 0;
+
+        // we can compute current set bit count using previous count
+        // as x/2 in O(1) time
+
+        // i%2 will be 0 for even number ans 1 for odd number
+
+        for (int i = 1; i <= n; ++i)
+            t[i] = t[i / 2] + i % 2;
+
+        return t;
+    }
 };