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Simplified solution for arrays_strings_better_compress #249

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Simplified solution for arrays_strings_better_compress #249

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129 changes: 42 additions & 87 deletions arrays_strings/compress_alt/better_compress_solution.ipynb
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Original file line number Diff line number Diff line change
Expand Up @@ -62,32 +62,26 @@
"source": [
"## Algorithm\n",
"\n",
"Since Python strings are immutable, we'll use a list of characters to build the compressed string representation. We'll then convert the list to a string.\n",
"\n",
"* Calculate the size of the compressed string\n",
" * Note the constraint about compressing only if it saves space\n",
"* If the compressed string size is >= string size, return string\n",
"* Create compressed_string\n",
" * For each char in string\n",
" * If char is the same as last_char, increment count\n",
"* For each char in string starting from index = 1\n",
" * If current char is the same as previous, increment count\n",
" * Else\n",
" * If the count is more than 2\n",
" * Append previous char to compressed_string\n",
" * Append count to compressed_string\n",
" * count = 1\n",
" * Else\n",
" * If the count is more than 2\n",
" * Append last_char to compressed_string\n",
" * append count to compressed_string\n",
" * count = 1\n",
" * last_char = char\n",
" * If count is 1\n",
" * Append last_char to compressed_string\n",
" * count = 1\n",
" * last_char = char\n",
" * If count is 2\n",
" * Append last_char to compressed_string\n",
" * Append last_char to compressed_string once more\n",
" * count = 1\n",
" * last_char = char\n",
" * Append last_char to compressed_string\n",
" * Append count to compressed_string\n",
" * Return compressed_string\n",
" * Append previous char count times to compressed_string\n",
"\n",
"* If the count is more than 2\n",
" * Append last char of string to compressed_string\n",
" * Append count to compressed_string\n",
"* Else\n",
" * Append last char of string count times to compressed_string\n",
"\n",
"* If the compressed string size is < string size\n",
" * Return compressed string\n",
"* Else\n",
" * Return string\n",
"\n",
"Complexity:\n",
"* Time: O(n)\n",
Expand All @@ -104,64 +98,31 @@
{
"cell_type": "code",
"execution_count": null,
"metadata": {
"collapsed": false
},
"metadata": {},
"outputs": [],
"source": [
"def compress_string(string):\n",
" if string is None or len(string) == 0:\n",
" return string\n",
"\n",
" # Calculate the size of the compressed string\n",
" size = 0\n",
" last_char = string[0]\n",
" for char in string:\n",
" if char != last_char:\n",
" size += 2\n",
" last_char = char\n",
" size += 2\n",
"\n",
" # If the compressed string size is greater than\n",
" # or equal to string size, return original string\n",
" if size >= len(string):\n",
" if string is None or len(string) < 3:\n",
" return string\n",
"\n",
" # Create compressed_string\n",
" # New objective:\n",
" # Single characters are to be left as is\n",
" # Double characters are to be left as are\n",
" compressed_string = list()\n",
" count = 0\n",
" last_char = string[0]\n",
" for char in string:\n",
" if char == last_char:\n",
" \n",
" count, compressed_string = 1, \"\"\n",
" \n",
" # shortcut for repetitive task\n",
" append = lambda c, k: c + str(k) if k > 2 else c * k\n",
" \n",
" for i in range(1, len(string)):\n",
" if string[i] == string[i-1]:\n",
" count += 1\n",
" else:\n",
" # Do the old compression tricks only if count exceeds two\n",
" if count > 2:\n",
" compressed_string.append(last_char)\n",
" compressed_string.append(str(count))\n",
" count = 1\n",
" last_char = char\n",
" # If count is either 1 or 2\n",
" else:\n",
" # If count is 1, leave the char as is\n",
" if count == 1:\n",
" compressed_string.append(last_char)\n",
" count = 1\n",
" last_char = char\n",
" # If count is 2, append the character twice\n",
" else:\n",
" compressed_string.append(last_char)\n",
" compressed_string.append(last_char)\n",
" count = 1\n",
" last_char = char\n",
" compressed_string.append(last_char)\n",
" compressed_string.append(str(count))\n",
" compressed_string += append(string[i-1], count)\n",
" count = 1\n",
"\n",
" # Convert the characters in the list to a string\n",
" return \"\".join(compressed_string)"
" compressed_string += append(string[-1], count)\n",
" \n",
" if len(compressed_string) < len(string):\n",
" return compressed_string\n",
" else:\n",
" return string"
]
},
{
Expand Down Expand Up @@ -201,9 +162,7 @@
{
"cell_type": "code",
"execution_count": null,
"metadata": {
"collapsed": true
},
"metadata": {},
"outputs": [],
"source": [
"def split_to_blocks(string):\n",
Expand Down Expand Up @@ -240,9 +199,7 @@
{
"cell_type": "code",
"execution_count": null,
"metadata": {
"collapsed": false
},
"metadata": {},
"outputs": [],
"source": [
"%%writefile test_compress.py\n",
Expand Down Expand Up @@ -272,9 +229,7 @@
{
"cell_type": "code",
"execution_count": null,
"metadata": {
"collapsed": false
},
"metadata": {},
"outputs": [],
"source": [
"%run -i test_compress.py"
Expand All @@ -297,9 +252,9 @@
"name": "python",
"nbconvert_exporter": "python",
"pygments_lexer": "ipython3",
"version": "3.5.0"
"version": "3.7.0"
}
},
"nbformat": 4,
"nbformat_minor": 0
"nbformat_minor": 1
}