Finding the Longest Common Prefix in an Array of Strings
The task is to identify the longest common prefix shared among all strings in a given array. For instance, with an input like ['abc', 'abcd', 'abd'], the result should be 'ab'.
Approach 1: Brute Force Itertaion
A straightforward method involves incrementally building prefixes and verifying each one against every string in the collection. We start with the shortest possible prefix and extend it character by character until we find a mismatch.
class Solution:
def longestCommonPrefix(self, strings):
if not strings:
return ''
base = strings[0]
result = ''
for position in range(len(base)):
candidate = base[:position + 1]
if all(s.startswith(candidate) for s in strings):
result = candidate
else:
break
return result
This approach has O(n²) time complexity, where n represents the combined length of all strings, as we check each prefix against every string in the array.
Approach 2: Sorting-Based Optimization
A more efficient strategy leverages sorted order. After sorting the strings lexicographically, the longest common prefix must exist between the first and last elements. This is because strings that share common characters will cluster to gether, and comparing only the extremes eliminates unnecessary comparisons.
class Solution:
def longestCommonPrefix(self, strings):
if not strings or not strings[0]:
return ''
sorted_strings = sorted(strings)
first_item = sorted_strings[0]
last_item = sorted_strings[-1]
common = ''
for idx in range(len(first_item)):
segment = first_item[:idx + 1]
if segment == last_item[:idx + 1]:
common = segment
else:
break
return common
The sorting step operates in O(n log n) time complexity using Python's Timsort algorithm. The subsequent prefix comparison runs in O(n) time, making this approach significantly faster for large datasets.
