Day 4: Swap bits at p and q positions program

Author: mandliya

README.md

@@ -6,8 +6,8 @@
 
 | Current Status|     Stats     |
 | :------------: | :----------: |
-| Total Problems | 139 |
-| Current Streak | 3 days |
+| Total Problems | 140 |
+| Current Streak | 4 days |
 | Longest Streak | 91 ( August 17, 2015 - November 15, 2015 ) |
 
 </center>
@@ -70,7 +70,8 @@ Include contains single header implementation of data structures and some algori
 | Given a number x and two positions (from right side) in binary representation of x, write a function that swaps n right bits at given two positions and returns the result. It is also given that the two sets of bits do not overlap.|[swapSetOfBits.cpp](bit_manipulation/swapSetOfBits.cpp)|
 | Add two numbers without using any arithmetic operators | [addition_without_operators.cpp](bit_manipulation/addition_without_operators.cpp)|
 |Louise and Richard play a game. They have a counter set to N. Louise gets the first turn and the turns alternate thereafter. In the game, they perform the following operations: <ul><li>If N is not a power of 2, reduce the counter by the largest power of 2 less than N.</li></ul><ul><li>If N is a power of 2, reduce the counter by half of N.</li></ul> The resultant value is the new N which is again used for subsequent operations.The game ends when the counter reduces to 1, i.e., N == 1, and the last person to make a valid move wins. <ul><li> Given N, your task is to find the winner of the game. If they set counter to 1, Richard wins, because its Louise' turn and she cannot make a move.</li></ul><ul><li>Input Format : -The first line contains an integer T, the number of testcases. T lines follow. Each line contains N, the initial number set in the counter.</ul></li> |[counter_game.cpp](bit_manipulation/counter_game.cpp)|
-|Determine if two integers are of opposite signs|[check_opposite_signs.cpp](bit_manipulation/check_opposite_signs.cpp)|
+|Determine if two integers are of opposite signs.|[check_opposite_signs.cpp](bit_manipulation/check_opposite_signs.cpp)|
+|Swap two bits at position p and q of a given integer.| [swapBits.cpp](bit_manipulation/swapBits.cpp)|
 
 
 ### Cracking the coding interview problems

bit_manipulation/swapBits.cpp

@@ -0,0 +1,39 @@
+#include <iostream>
+#include <bitset>
+
+int swapBits(int n, int p, int q)
+{
+    if (p == q)
+    {
+        return n;
+    }
+    // If bits are same, no point swapping.
+    // Determine if bits are different
+    //
+    if (((n & (1 << p)) >> p) ^ ((n & (1 << q)) >> q))
+    {
+        // toggle bits at p and q positions
+        //
+        n ^= (1 << p);
+        n ^= (1 << q);
+    }
+
+    return n;
+}
+
+int main()
+{
+    int n, p, q;
+    std::cout << "Enter a number: ";
+    std::cin >> n;
+    std::cout << "Enter bit position 1:";
+    std::cin >> p;
+    std::cout << "Enter bit position 2:";
+    std::cin >> q;
+    int r = swapBits(n, p, q);
+    std::cout << "Number before swap :" << n << " (" << std::bitset<8>(n).to_string() << ") "
+        << std::endl <<  "Number after swapping bits at position "
+        << p << " and " << q << " : "  << r << " (" << std::bitset<8>(r) << ")"
+        << std::endl;
+    return 0;
+}