[LeetCode] Longest Common Prefix

Problem

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

Note

我的思路是用StringBuilder对strs中的字符串逐个遍历第i位的字符，如果都相同，就把这个字符存入sb，否则返回已有的sb字符串。
注意，第二层for循环的条件：i的值不能大于str.length()-1。

Solution

class Solution {
    public String longestCommonPrefix(String[] strs) {
        if (strs == null || strs.length == 0) return "";
        int len = strs[0].length();
        StringBuilder sb = new StringBuilder();
        for (int i = 0; i < len; i++) {
            for (String str: strs) {
                if (str.length() < i+1 || str.charAt(i) != strs[0].charAt(i)) {
                    return sb.toString();
                }
            }
            sb.append(strs[0].charAt(i));
        }
        return sb.toString();
    }
}

Update 2018-8

class Solution {
    public String longestCommonPrefix(String[] strs) {
        if (strs == null || strs.length == 0) return "";
        Arrays.sort(strs);
        //compare strs[0] and strs[strs.length-1], since they should be the most different pair
        int i = 0, len = strs.length;
        while (i < Math.min(strs[0].length(), strs[len-1].length()) && strs[0].charAt(i) == strs[len-1].charAt(i)) {
            i++;
        }
        return strs[0].substring(0, i);
    }
}