https://leetcode-cn.com/problems/longest-common-prefix/description/
我的解决方案：

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

解决方案二：参考了耗时最短的代码，使用二分法，并结合Java.lang.String.StartWith方法判断给定字符串是否为另一字符串的前缀

class Solution {
    public String longestCommonPrefix(String[] strs) {
        if (strs == null || strs.length == 0)
            return "";
        int minLen = Integer.MAX_VALUE;
        for (String str : strs)
            minLen = Math.min(minLen, str.length());
        int low = 1;
        int high = minLen;
        while (low <= high) {
            int middle = (low + high) / 2;
            if (isCommonPrefix(strs, middle))
                low = middle + 1;
            else
                high = middle - 1;
        }
        return strs[0].substring(0, (low + high) / 2);
    } 

    private boolean isCommonPrefix(String[] strs, int len){
        String str1 = strs[0].substring(0,len);
        for (int i = 1; i < strs.length; i++)

            if (!strs[i].startsWith(str1))
                return false;
        return true;
    }
}