[Leetcode 18] 14 Longest Common Prefix

Problem:

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

Analysis:

Each time take a character from the first string and compare it with other strings' same position character.

If reaching some end of some string or find a mismatch, then the longest common prefix has been found, just return.

Take some corner cases into considerations([], [""]).

Time Complexity O(n*m), n is the strings in the given input, m is the prefix compared when existing. The worst case for m is length of the shortest string in the array.

Space Complexity O(l), l is the total characters in the String array.

Code:

public class Solution {
    public String longestCommonPrefix(String[] strs) {
        // Start typing your Java solution below
        // DO NOT write main() function
        if (strs.length == 0 || strs[0].length() == 0)
            return "";
            
        int pos = 0;
        char ch = 'c';
        String s0 = strs[0];
        while (true) {
            if (pos == s0.length())
                return s0.substring(0, pos);
            
            ch = s0.charAt(pos);
            for (String s : strs) {
                if (pos == s.length() || ch!=s.charAt(pos))
                    return s0.substring(0, pos);
            }
            
            pos += 1;
        }
    }
}

Attention:

Don't know why in JudgeLarge, sometimes will have Time Limit Exceeded error but sometimes will AC. May be problems in testing environment.