14. Longest Common Prefix

 1 public class Solution {
 2     public string LongestCommonPrefix(string[] strs) {
 3         int length = strs.Length;
 4         if (length == 0) return string.Empty;
 5         string result = strs[0];
 6         for (int i = 1; i < length; i++)
 7         {
 8             result = GetPrefix(strs[i], result);
 9             if (string.IsNullOrEmpty(result)) break;
10         }
11         return result;
12     }
13     
14     private string GetPrefix(string s1, string s2)
15     {
16         StringBuilder prefix = new StringBuilder();
17         int minLen = Math.Min(s1.Length, s2.Length);
18         for (int i = 0; i < minLen; i++)
19         {
20             if (s1[i].Equals(s2[i]))
21             {
22                 prefix.Append(s1[i]);
23             }
24             else
25             {
26                 break;
27             }
28         }
29         return prefix.ToString();
30     }
31 }

 1 public class Solution {
 2     public string LongestCommonPrefix(string[] strs) {
 3         int length = strs.Length;
 4         if (length == 0) return string.Empty;
 5         for (int i = 0; i < strs[0].Length; i ++)
 6         {
 7             for (int j = 1; j < length; j ++)
 8             {
 9                 if (i == strs[j].Length || strs[j][i] != strs[0][i])
10                 {
11                     return strs[0].Substring(0, i);
12                 }
13             }
14         }
15         return strs[0];
16     }
17 }