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Task 1: "Character Swapping
You are given a string $S of size $N.
You are also given swap count $C and offset $O such that $C >= 1, $O >=
1, $C <= $O and $C + $O <= $N.
Write a script to perform character swapping like below:
for i = 1 to $C
S[ i % N ] <=> S[ (i + O) % N ]
Example 1
Input:
$S = 'perlandraku'
$C = 3
$O = 4
01234567890
perlandraku
Character Swapping:
swap 1: pos 1 and 5: e <=> n = pnrlaedraku
swap 2: pos 2 and 6: r <=> d = pndlaerraku
swap 3: pos 3 and 7: l <=> r = pndraerlaku
Output:
pndraerlaku
"
My notes: ok. none of $i % N (for i=1..$C) needs the % N
given that $C + $O <= $N and min $O is 1. So that becomes:
for i = 1 to $C
S[ i ] <=> S[ (i + O) % N ]
and the only one of the (i + O) % N expressions that may need
the % N part is i=C, when C+O == N. Of course i + O increments
so pre-calculate it, and set it back to 0 hit it hits N.
Task 2: "Gray Code Sequence
You are given an integer 2 <= $N <= 5.
Write a script to generate $N-bit gray code sequence.
2-bit Gray Code Sequence: [0, 1, 3, 2]
To generate the 3-bit Gray code sequence from the 2-bit Gray code sequence,
follow the step below:
2-bit Gray Code sequence: [0, 1, 3, 2]
Binary form of the sequence a) S1 = [00, 01, 11, 10]
Reverse of S1 b) S2 = [10, 11, 01, 00]
Prefix all entries of S1 with '0' c) S1 = [000, 001, 011, 010]
Prefix all entries of S2 with '1' d) S2 = [110, 111, 101, 100]
Concatenate S1 and S2 gives 3-bit Gray Code sequence
e) [000, 001, 011, 010, 110, 111, 101, 100]
Now convert them back to decimal:
3-bit Gray Code sequence [0, 1, 3, 2, 6, 7, 5, 4]
Example
Input: N = 4
Output: [0, 1, 3, 2, 6, 7, 5, 4, 12, 13, 15, 14, 10, 11, 9, 8]
"
My notes: ok. However, there's no point in taking the original N-1-bit gray
code sequence, converting it to binary, prepending zeroes and converting it
back to decimal - because leading zeroes don't change the decimal numbers.
So the first half of the N-bit gray code sequence is simply the N-1-bit gray
code sequence.
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