# 14 Longest Common Prefix – Easy

### Problem:

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

### Thoughts:

Get the first string in the array of strings, the longest common prefix is at best this first string.

So iterate over all strings, and find out if there is a common prefix for the current string and current prefix.

If the first string length is m, and there are n strings. This method will be O(mn) running time.

There could be a optimized solution. Instead of always start with the first string in the array, init the prefix to be the shortest string in the array. If k is the shortest string’s length, then running time would be O(kn). This is helpful when k is significantly smaller than m, where m is the first string length.

### Solutions:

``````public class Solution {
public String longestCommonPrefix(String[] strs) {
if (strs.length == 0) {
return "";
}
String prefix = strs;
for (int i = 1; i < strs.length; i ++ ) {
for (int j = 0; j < prefix.length(); j ++){
if (j == strs[i].length() || prefix.charAt(j) != strs[i].charAt(j)) {
prefix = prefix.substring(0, j);
break;
}
}
}
return prefix;
}
}
``````