5.6. conversion

05. Bit manipulation/5.6. Conversion.md

@@ -0,0 +1,32 @@
+# 5.6. Conversion
+
+> Write a function to determine the number of bits you would need to flip to convert integer A to integer B
+
+Input: 29 (or: 11101), 15 (or: 01111)
+Output: 2
+
+First need to convert to array of bits, right? Levenstein distance between them. Or just iterate the bits by doing num >> 1, get rightmost bit of both nums and do XOR. Sum up all numbers.
+
+## Hints
+
+> How would you figure out how many bits are different between two numbers?
+
+Levenstein distance between the strings, but we're working with numbers. Iterate all bits and add up the differences.
+
+> Think about what an XOR indicates. If you do a XOR b, where does the result have 1s? Where does it have Os?
+
+XOR has result 0 if bits are different, 1 if bits are same.
+
+## Solution
+
+a ^ b makes XOR between a and b, then just iterate a c and increase count if the value at that point is 1. Then shift c to right, keep deleting the right most bit.
+
+```c++
+int bitSwapRequired(int a, int b) {
+    int count = 0;
+    for (int c = a ^ b; c != 0; c = c >> 1) {
+        count += c & 1;
+    }
+    return count;
+}
+```

README.md

@@ -55,6 +55,7 @@ If you can't afford to buy the book, you can find a free pdf [here](http://ahmed
 * Binary to string
 * Flip bit to create longest sequence of 1s
 * (( n & (n-1)) == 0). n=?
+* How many different bits do two numbers have. 11001 vs. 11010 = 2. Levenstein distance
 
 ## Chapter 7 Object-oriented design