day 25: 338-valid-counting-bits, 167-two-sum-ii-input-array-is-sorted

338-counting-bits/driver.cpp

@@ -0,0 +1,10 @@
+#include "soln.hpp"
+
+int main()
+{
+	int n = 7;
+	vector<int> answer{0, 1, 1, 2, 1, 2, 2, 3};
+	Solution soln;
+	cout << "Counted bits correctly? " << soln.test(n, answer) << endl;
+	return 0;
+}

338-counting-bits/soln.cpp

@@ -0,0 +1,37 @@
+#include "soln.hpp"
+
+vector<int> Solution::countBits(int n)
+{
+	vector<int> result(n + 1);
+	// // O(n log n) approach, naive
+	// // O(n)
+	// int num;
+	// for(int i = 0; i <= n; i++)  {
+	//     num = i;
+	//     // O(log n)
+	//     while(num)    {
+	//         result[i] += num&1;
+	//         num=num>>1;
+	//     }
+	// }
+
+	// O(n) approach
+	result[0] = 0;
+	if (n == 0)
+	{
+		return result;
+	}
+	for (int i = 1; i < n + 1; i = i * 2)
+	{
+		for (int j = i; (j < i * 2) && (j < n + 1); j++)
+		{
+			result[j] = result[(j / i) + (j - i) - 1] + 1;
+		}
+	}
+	return result;
+}
+
+bool Solution::test(int n, vector<int> &answer)
+{
+	return countBits(n) == answer;
+}

338-counting-bits/soln.hpp

@@ -0,0 +1,8 @@
+#include <bits/stdc++.h>
+using namespace std;
+class Solution
+{
+public:
+	vector<int> countBits(int n);
+	bool test(int n, vector<int> &answer);
+};