count set bit from 1 to N

Author: raunakpandey1

Bit Manipulation/Count_total_set_bits.cpp

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+
+/*
+You are given a number N. Find the total count of set bits for all numbers from 1 to N(both inclusive).
+
+Example 1:
+
+Input: N = 4
+Output: 5
+Explanation:
+For numbers from 1 to 4.
+For 1: 0 0 1 = 1 set bits
+For 2: 0 1 0 = 1 set bits
+For 3: 0 1 1 = 2 set bits
+For 4: 1 0 0 = 1 set bits
+Therefore, the total set bits is 5.*/
+
+#include<bits/stdc++.h>
+using namespace std;
+ 
+// Function to count set bits in the given number x
+// n: input to count the number of set bits
+int largestpowerof2inrange(int n)
+{
+    int x=0;
+    while((1<<x) <=n)
+    {
+        x++;
+    }
+    return x-1;
+}
+int countSetBits(int n)
+{
+    // Your logic 
+    if(n==0) return 0;
+    int x=largestpowerof2inrange(n);
+    int first= x*(1<<(x-1));
+    int second= n-(1<<x)+1;
+    int third=n-(1<<x);
+    int ans=first+second+countSetBits(third);
+    return ans;
+}
+ 
+// Driver code
+int main()
+{
+	 int t;
+	 cin>>t;// input testcases
+	 while(t--) //while testcases exist
+	 {
+	       int n;
+	       cin>>n; //input n
+	       
+	       cout << countSetBits(n) << endl;// print the answer
+	  }
+	  return 0;
+}
+  // } Driver Code Ends