14. Longest Common Prefix(easy)

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

If there is no common prefix, return an empty string "".

Example 1:

Input: ["flower","flow","flight"]
Output: "fl"
Example 2:

Input: ["dog","racecar","car"]
Output: ""
Explanation: There is no common prefix among the input strings.
Note:

All given inputs are in lowercase letters a-z.

分析：从字符串数组中找出公共的前缀。取第一个字符串和其余的字符串进行比较，从第一个字符开始，比较每一个字符串，只要发现字符不同或者字符越界，直接返回结果。

public static String longestCommonPrefix(String[] strs) {
        if (strs.length == 0) {
            return "";
        }
        StringBuilder sb = new StringBuilder();
        String firstStr = strs[0];
        boolean flag = true;
        for (int i = 0; i < firstStr.length(); i++) {
            for (int j = 1; j < strs.length; j++) {
                if (i == strs[j].length()) {
                    flag = false;
                    break;
                }
                if (strs[j].charAt(i) != firstStr.charAt(i)) {
                    flag = false;
                    break;
                }
            }
            if (flag == true) {
                sb.append(firstStr.charAt(i));
            } else {
                break;
            }
        }
        return sb.toString();
    }