14. Longest Common Prefix (String - Horizontal Scanning) 20.2.4 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: ["flower","flow","flight"]
Output: "fl"
Example 2:

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

All given inputs are in lowercase letters a-z.

Solution: -------------------------------------------- String - Horizontal Scanning
------------------------------------------------------ O(S) T, where S is the sum of all characters in all strings, O(1) S
class Solution(object):
    def longestCommonPrefix(self, strs):
        """
        :type strs: List[str]
        :rtype: str
        """
        if len(strs) == 0:
            return ""
        res = strs[0]
        for i in range(1, len(strs)):                             # Traverse the entire strs
            while not res in strs[i] or strs[i].index(res) != 0:  # Must add "not res in strs[i]" for non-existing cases
                                                                  # if we do not add "not res in strs[i]", 
                                                                  # will bring "substring not found" error,
                                                                  # because .index() for string in Python requires the substring to exist
                res = res[:(len(res) - 1)]                        # if not satisfied, reduce the res from the right by one character
                if res == "":                                     # No LCP at all, return directly
                    return ""
        return res

Java Version:
class Solution {
    public String longestCommonPrefix(String[] strs) {
        if (strs == null || strs.length == 0) {
            return "";
        }
        
        String prefix = strs[0];
        
        for (int i = 1; i < strs.length; i ++) {
            while (strs[i].indexOf(prefix) != 0) {
                prefix = prefix.substring(0, prefix.length() - 1);
                if (prefix.length() == 0) {
                    return "";
                }
            }
        }
        
        return prefix;
        
    }
}