#14.Longest Common Prefix
Problem statement
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: strs = ["flower","flow","flight"]
Output: "fl"
Example 2
Input: strs = ["dog","racecar","car"]
Output: ""
Explanation: There is no common prefix among the input strings.
Explanation
找出陣列中所有元素最長的相同字符並返回，如果沒有相同字符則返回空字串 ""。
例如 cat 和 carry 相同的前綴字符為 ca
Solution
用雙迴圈逐一比對，第一層遍歷元素長度，第二層則遍歷陣列內所有元素。
但是找尋陣列內元素時，不可使用超出元素長度的索引，故先找到陣列內最短長度的元素，再以此長度作為第一層迴圈的中止值。
public string LongestCommonPrefix(string[] strs)
{
if (strs.Length == 0) return null;
string res = string.Empty;
string str = strs[0];
foreach (var s in strs)
{
if (s.Length < str.Length)
str = s;
}
int len = strs.Length;
for (int i = 0; i < str.Length; i++)
{
for (int j = 0; j < len; j++)
{
if (str[i] == strs[j][i])
continue;
else
return res;
}
res += str[i];
}
return res;
}
Reference
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