[Python] Performance enhance by not using range() for comparison

When I was trying to enhance the performance of my Python code, the frist thing I tried is reducing the usage of functions. After I substituted the range() function, the performance had improved a lot, from 404ms to 106ms. The following is the difference between the two versions of the "ZigZag Conversion" code.

404ms

	class Solution:
	# @return a string
	def convert(self, s, nRows):
	row_len = 2 * nRows - 2
	string = ["" for _ in range(nRows)]
	if nRows <= 2:
	for i in range(len(s)):
	string[i % nRows] += s[i]
	else:
	for i in range(len(s)):
	res = i % row_len
	if res in range(nRows, row_len):
	string[row_len - res] += s[i]
	else:
	string[res] += s[i]
	output = ""
	for i in range(nRows):
	output += string[i]
	return output

view raw ZigZag_404.py hosted with ❤ by GitHub

106ms

	class Solution:
	# @return a string
	def convert(self, s, nRows):
	row_len = 2 * nRows - 2
	string = ["" for _ in range(nRows)]
	if nRows <= 2:
	for i in range(len(s)):
	string[i % nRows] += s[i]
	else:
	for i in range(len(s)):
	res = i % row_len
	if res >= nRows and res < row_len: # I just replaced the range() function here
	string[row_len - res] += s[i]
	else:
	string[res] += s[i]
	output = ""
	for i in range(nRows):
	output += string[i]
	return output

view raw ZigZag_106.py hosted with ❤ by GitHub

Although the performance result depends on the test data, this substitution really improves the entire performance.