Task 1: "Caesar Cipher

You are given string $S containing alphabets A..Z only and a number $N.

Write a script to encrypt the given string $S using Caesar Cipher with
left shift of size $N.

Example

	Input: $S = "THE QUICK BROWN FOX JUMPS OVER THE LAZY DOG", $N = 3
	Output: "QEB NRFZH YOLTK CLU GRJMP LSBO QEB IXWV ALD"

	Plain:    ABCDEFGHIJKLMNOPQRSTUVWXYZ
	Cipher:   XYZABCDEFGHIJKLMNOPQRSTUVW

	Plaintext:  THE QUICK BROWN FOX JUMPS OVER THE LAZY DOG
	Ciphertext: QEB NRFZH YOLTK CLU GRJMP LSBO QEB IXWV ALD

"

My notes: ah, the good old Caesar cipher, aka rotN..  easy.


Task 2: "Binary Substrings

You are given a binary string $B and an integer $S.

Write a script to split the binary string $B of size $S and then find
the minimum number of flips required to make it all the same.

Example 1:

	Input: $B = "101100101" $S = 3
	Output: 1

	Binary Substrings:
	    "101": 0 flip
	    "100": 1 flip to make it "101"
	    "101": 0 flip

Example 2:

	Input $B = "10110111" $S = 4
	Output: 2

	Binary Substrings:
	    "1011": 0 flip
	    "0111": 2 flips to make it "1011"
"

My notes:  hmm.. this could be specified a LOT more clearly.  bad phrasing!
and the examples don't completely clarify what we're supposed to do.
The first task is obvious: split BS into "length S" chunks - that's trivial..

But then what we do with the chunks is not quite clear - both examples seem
to show taking the first chunk as the "goal to reach" and then all we
do is to find out the maximum number of bits that have to be flipped to turn
any of the OTHER chunks into the goal-chunk.  But what's special about the
first chunk?  Also, if we do that, where does the word "minimum" come in?

I wonder whether it means, instead:
- try each distinct chunk as the goal chunk, for each such goal, find the
  maximum number of bits that have to be flipped to turn chunkN into the
  goalchunk, AND THEN FIND THE MINIMUM OF ALL THOSE MAXIMUMS.

I'm going to assume that it's the latter..  Update: having coded it, yes,
this can produce different answers than "first chunk is the goal".
The following example demonstrates the difference:

Example dcw-1:
	Input: $B = "000101011111" $S = 3
	Output: 2

	Binary Substrings:
	000
	101
	011
	111

 If 000 is the goal, then we'd work out how many bits have to be
 flipped in each of the other substrings to reach 000, getting:
	Binary Substrings:
	000: 0 flips to teach 000
	101: 2 flips to teach 000
	011: 2 flips to teach 000
	111: 3 flips to teach 000
 max those is 3.

 But if 101 is the goal, we'd have:
	Binary Substrings:
	000: 2 flips to teach 101
	101: 0 flips to teach 101
	011: 2 flips to teach 101
	111: 1 flip to teach 101
 let's abbreviate that as: goal: 101: flips=2,0,2,1
 max those is 2.

 If 011 is the goal, we get flips=2,2,0,1, max 2.

 Finally, if 111 is the goal, we get flips=3,1,1,0, max 3

 So the MINIMUM of all those maximums is: min(3,2,2,3) = 2.
 That's the answer!