Important Bitmasking algorithms added!

Author: rohit-bindal

Bitmasking/1. Unique number I.txt

@@ -0,0 +1,26 @@
+#include <bits/stdc++.h>
+using namespace std;
+
+/*
+Every number occurs twice in the array except one number
+find out that number
+*/
+
+int uniqueNumber(int ar[], int n)
+{
+	int ans = 0;
+	for(int i=0; i<n; i++)
+	{
+		ans = ans ^ ar[i];
+	}
+	return ans;
+}
+
+int main()
+{
+	int arr[]= {1,5,3,5,8,9,8,1,3};
+    int n = sizeof(arr)/sizeof(int);
+
+	cout<<uniqueNumber(arr, n);
+	return 0;
+}

Bitmasking/10. Unique Number III.txt

@@ -0,0 +1,41 @@
+#include <bits/stdc++.h>
+using namespace std;
+
+/*
+Every number is occuring thrice in the given array except one. find the unique number
+*/
+
+int main()
+{
+  int count[64] = {0};
+
+  int n;
+  cin>>n;
+  int no;
+  for(int i=0; i<n; i++)
+  {
+    cin>>no;
+    //we will keep adding the bits of upcoming numbers in the count array
+
+    int j=0;
+    while(no>0)
+    {
+      count[j]+= (no&1);
+      j++;
+      no = no>>1;
+    }
+  }
+
+  //now lets take mod with 3 of numbers present in the count array 
+  int ans = 0;
+  int p = 1;
+  for(int i=0; i<n; i++)
+  {
+    count[i] = count[i]%3;
+    ans+=count[i]*p;
+    p*=2;
+  }
+  cout<<ans;
+
+	return 0;
+}

Bitmasking/11. Fast Exponentiation.txt

@@ -0,0 +1,27 @@
+#include <bits/stdc++.h>
+using namespace std;
+
+int fastExponentiation(int a, int n)
+{
+  int ans = 1;
+
+  while(n>0)
+  {
+    if((n&1)==1)
+    {
+      ans*=a;
+    }
+    n>>=1; 
+    a*=a;
+  }
+  return ans;
+}
+
+int main()
+{
+  
+  int a,n;
+  cin>>a>>n;
+  cout<<fastExponentiation(a,n);
+	return 0;
+}

Bitmasking/12. generate subsets.txt

@@ -0,0 +1,34 @@
+#include <bits/stdc++.h>
+using namespace std;
+
+void filterChars(char c[], int n)
+{
+  int j=0;
+  while(n>0)
+  {
+    if(n&1)
+    {
+      cout<<c[j];
+    }
+    j++;
+    n>>=1;
+  }
+  cout<<endl;
+}
+
+void printSubsequences(char c[])
+{
+  int n = strlen(c);
+  for(int i=0; i<(1<<n); i++)
+  {
+    filterChars(c,i);
+  }
+}
+
+int main()
+{
+  char c[100];
+  cin>>c;
+  printSubsequences(c);
+	return 0;
+}

Bitmasking/13. codechef problem.txt

@@ -0,0 +1,81 @@
+#include <bits/stdc++.h>
+using namespace std;
+ 
+#define IOS ios::sync_with_stdio(0); cin.tie(0); cout.tie(0);
+#define endl "\n"
+#define int long long
+
+/*
+problem link:
+https://www.codechef.com/COOK128B/problems/OROFAND
+*/
+
+int32_t main()
+{
+  IOS;
+  int t;
+  cin>>t;
+  while(t--)
+  {
+    int n,q;
+    cin>>n>>q;
+
+    int arr[n];
+    for(int i=0; i<n; i++)
+    {
+      cin>>arr[i];
+    }
+
+    int bit[32] = {0};
+    for(int i=0; i<n; i++)
+    {
+      for(int j=0; j<32; j++)
+      {
+        if((1<<j)&arr[i]) bit[j]++;
+      }
+    }
+
+    int ans = 0;
+    for(int i=0; i<32; i++)
+    {
+      if(bit[i]>0)
+      {
+        ans+=(1<<i);
+      }
+    }
+
+    cout<<ans<<endl;
+
+    while(q--)
+    {
+      int x,v;
+      cin>>x>>v;
+      x--;
+
+      for(int i=0; i<32; i++)
+      {
+        if(((1<<i)&arr[x]))
+        bit[i]--;
+      }
+
+      arr[x]=v;
+
+      for(int i=0; i<32; i++)
+      {
+        if(((1<<i)&v)) bit[i]++;
+      }
+
+      ans = 0;
+      for(int i=0; i<32; i++)
+      {
+        if(bit[i]>0)
+        {
+          ans+=(1<<i);
+        }
+      }
+      cout<<ans<<endl;
+    }
+  }
+  return 0;
+}
+

Bitmasking/2. get ith bit.txt

@@ -0,0 +1,20 @@
+#include <bits/stdc++.h>
+using namespace std;
+
+//task is to find ith bit (i starting from zero and from right side) in a number
+
+int ithBit(int n, int i)
+{
+	int mask = 1<<i;
+	int bit = (n & mask) > 0 ? 1 : 0;
+
+	return bit;
+}
+
+int main()
+{
+	int n,i;
+	cin>>n>>i;
+    cout<<ithBit(n,i);
+	return 0;
+}

Bitmasking/2. set ith bit.txt

@@ -0,0 +1,18 @@
+#include <bits/stdc++.h>
+using namespace std;
+
+int setIthBit(int n, int i)
+{
+	int mask = 1<<i;
+	n = n | mask;
+
+	return n;
+}
+
+int main()
+{
+	int n,i;
+	cin>>n>>i;
+    cout<<setIthBit(n,i);
+	return 0;
+}

Bitmasking/3. clear ith bit.txt

@@ -0,0 +1,18 @@
+#include <bits/stdc++.h>
+using namespace std;
+
+int clearIthBit(int n, int i)
+{
+	int mask = ~(1<<i);
+	n = n & mask;
+
+	return n;
+}
+
+int main()
+{
+	int n,i;
+	cin>>n>>i;
+    cout<<clearIthBit(n,i);
+	return 0;
+}

Bitmasking/4. update ith bit by value(0 or 1).txt

@@ -0,0 +1,23 @@
+#include <bits/stdc++.h>
+using namespace std;
+
+int updateIthBitByValue(int n, int i, int v)
+{
+   //lets first cleat ith bit
+   int mask = (~(1<<i));
+   n = (n&mask);
+
+   int newmask = (v<<i);
+   n = (n|newmask);
+
+   return n;
+}
+
+int main()
+{
+  int n,i,v;
+  cin>>n>>i>>v;
+
+  cout<<updateIthBitByValue(n,i,v);
+	return 0;
+}

Bitmasking/5. clear last i bits of a number.txt

@@ -0,0 +1,24 @@
+#include <bits/stdc++.h>
+using namespace std;
+
+int clearLastIBits(int n, int i)
+{
+	//lets take mask with all ones
+	int mask = -1;
+
+	//lets clear last i bits of our mask
+	mask = (mask<<i);
+
+	//take AND with of your number with mask
+	n = n&mask;
+
+	return n;
+}
+
+int main()
+{
+	int n,i;
+	cin>>n>>i;
+	cout<<clearLastIBits(n,i);
+	return 0;
+}

Bitmasking/6. clear bits from ith index to jth (from right to left).txt

@@ -0,0 +1,26 @@
+#include <bits/stdc++.h>
+using namespace std;
+
+int clearBitsFromItoJ(int n, int i, int j)
+{
+	//lets take one mask (a) as all ones with j+1 number of trailing zeros
+	int a = (~0)<<(j+1);
+
+	//lets take mask (b) as all zero with i number of trailing ones
+	int b = (1<<i)-1;
+
+	//required mask will be a|b
+	int mask = a|b;
+
+	n = n&mask;
+
+	return n;
+}
+
+int main()
+{
+	int n,i,j;
+	cin>>n>>i>>j;
+	cout<<clearBitsFromItoJ(n,i,j);
+	return 0;
+}

Bitmasking/7. Replace bits in N by M.txt

@@ -0,0 +1,28 @@
+#include <bits/stdc++.h>
+using namespace std;
+
+int replaceNbitsByMFromItoJ(int n, int m, int i, int j)
+{
+  //lets first clear the bits in n from i to j
+  int a = (~0)<<(j+1);
+
+  int b = (1<<i) -1;
+  int mask = a|b;
+
+  n = n&mask;
+
+  m = (m<<i);
+
+  return n|m;
+}
+
+int main()
+{
+	int n = 15;
+	int m = 2;
+	int i = 1;
+	int j = 3;
+
+	cout<<replaceNbitsByMFromItoJ(n,m,i,j);
+	return 0;
+}