leetcode - 14. Longest Common Prefix

Description

Write a function to find the longest common prefix string amongst an array of strings.

If there is no common prefix, return an empty string “”.

Example 1:

Input: strs = ["flower","flow","flight"]
Output: "fl"

Example 2:

Input: strs = ["dog","racecar","car"]
Output: ""
Explanation: There is no common prefix among the input strings.

Constraints:

1 <= strs.length <= 200
0 <= strs[i].length <= 200
strs[i] consists of only lowercase English letters.

Solution

Simulation

Time complexity: $o(str.len\ast len(strs))$
Space complexity: $o(1)$

Sort

Sort the strings lexicographically, and compare the first and last.

Code

Simulation

class Solution:
    def longestCommonPrefix(self, strs: List[str]) -> str:
        res = 1
        min_len = min(len(i) for i in strs)
        while res <= min_len:
            cur_prefix = strs[0][:res]
            same_flag = True
            for i in range(1, len(strs)):
                same_flag &= cur_prefix == strs[i][:res]
            if not same_flag:
                break
            res += 1
        return strs[0][:res - 1]

Sort

class Solution:
    def longestCommonPrefix(self, strs: List[str]) -> str:
        strs.sort()
        res = ''
        first, last = strs[0], strs[-1]
        for i in range(len(first)):
            if first[i] == last[i]:
                res += first[i]
            else:
                break
        return res