Thinking process - I

public class Solution {
    public String longestCommonPrefix(String[] strs) {
        if (strs == null || strs.length == 0) return "";
        if (strs.length == 1) return strs[0];

        int endIndex = 0;
        int strIndex = 1;

        while (endIndex < strs[strIndex].length()) {
            if (endIndex >= strs[strIndex - 1].length() || strs[strIndex].charAt(endIndex) != strs[strIndex - 1].charAt(endIndex)) break;

            strIndex++;
            if (strIndex == strs.length) {
                strIndex = 1;
                endIndex++;
            }
        }

        return strs[0].substring(0, endIndex);   
    }
}

Thinking process - II

public class Solution {
    public String longestCommonPrefix(String[] strs) {
        if (strs == null || strs.length == 0) return "";

        String prev = strs[0];
        int strIndex = 1;

        while (strIndex < strs.length) {
            while (strs[strIndex].indexOf(prev) != 0) {//not common prefix
                prev = prev.substring(0, prev.length() - 1);
            }

            strIndex++;
        }

        return prev; 
    }
}