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zigzag_conversion.py
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61 lines (46 loc) · 1.37 KB
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'''
ZigZag Conversion
The string "PAYPALISHIRING" is written in a zigzag pattern on a given number of rows like this: (you may want to display this pattern in a fixed font for better legibility)
P A H N
A P L S I I G
Y I R
And then read line by line: 'PAHNAPLSIIGYIR'
Input: s = 'PAYPALISHIRING', num_rows = 3
Output: 'PAHNAPLSIIGYIR'
=========================================
Go row by row and using the steps logic build the new string by jumping chars.
Middle rows have 2 times more elements than the first and last row.
Time Complexity: O(N)
Space Complexity: O(N)
'''
############
# Solution #
############
def convert(s, num_rows):
if num_rows == 1:
return s
n = len(s)
res = ''
cycle = 2 * (num_rows - 1)
for i in range(0, num_rows):
steps = cycle - 2 * i
if (i == 0) or (i == num_rows - 1):
# if first or last row, make a whole cycle
steps = cycle
j = i
while j < n:
res += s[j]
j += steps
if (i > 0) and (i < num_rows - 1):
# change the steps if not first or last row
steps = cycle - steps
return res
###########
# Testing #
###########
# Test 1
# Correct result => 'PAHNAPLSIIGYIR'
print(convert('PAYPALISHIRING', 3))
# Test 2
# Correct result => 'PINALSIGYAHRPI'
print(convert('PAYPALISHIRING', 4))