14. Longest Common Prefix

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

写一个函数（或方法）来寻找一个字符串数组中的最长公共前缀。

注释

"abcdefg"
"abcdefghijk"
"abcdfghijk"
"abcef"

上面的字符串数组的最长公共前缀就是"abc"。

    public String longestCommonPrefix(String[] strs) {
        if(strs == null || strs.length == 0)    return "";
        String pre = strs[0];
        int i = 1;
        while(i < strs.length){
            while(strs[i].indexOf(pre) != 0)
                pre = pre.substring(0,pre.length()-1);
            i++;
        }
        return pre;        
    }