LeetCode link: 14. Longest Common Prefix, difficulty: Easy.
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 <= 2000 <= strs[i].length <= 200strs[i]consists of only lowercase English letters if it is non-empty.
Intuition
- To find the longest common prefix, you can scan from left to right, using the characters of the first string as the baseline.
- If the current character in the other strings does not match the baseline character, return the result. After each round of iteration, add the baseline character to the common prefix.
Complexity
Time complexity
O(M * N)
Space complexity
O(1)
Ruby #
# @param {String[]} strs
# @return {String}
def longest_common_prefix(strs)
result = ''
(0...strs[0].size).each do |i|
char = strs[0][i]
strs[1..].each do |str|
if str[i] != char
return result
end
end
result << char
end
result
end
Python #
class Solution:
def longestCommonPrefix(self, strs: List[str]) -> str:
result = ''
for i in range(len(strs[0])):
char = strs[0][i]
for string in strs[1:]:
if i >= len(string) or string[i] != char:
return result
result += char
return result
Java #
class Solution {
public String longestCommonPrefix(String[] strs) {
var result = "";
for (var i = 0; i < strs[0].length(); i++) {
var c = strs[0].charAt(i);
for (var j = 1; j < strs.length; j++) {
if (i >= strs[j].length() || strs[j].charAt(i) != c) {
return result;
}
}
result += c;
}
return result;
}
}