找出陣列裡元素的重複字元，沒有共同重複字元則回傳空字串。
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.
解法: 以陣列第一個元素當作prefix，把此prefix跟陣列所有元素比較，如果沒有則去除prefix字元再重複比較，直到所有元素皆比較完。
public class Solution {
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;
}
}
Ref: