14. Longest Common Prefix

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

題意，找到一組字符串中共同的公共前綴，只需要簡(jiǎn)單的遍歷即可

c++代碼：

class Solution {  
public:  
    string longestCommonPrefix(vector<string> &strs) {  
        if (strs.empty())  
            return "";  
        for (int i = 0; i < strs[0].length(); i++) {  
            for (int j = 1; j < strs.size(); j++)  
                if (i >= strs[j].length() || strs[j][i] != strs[0][i])  
                    return strs[0].substr(0, i);  
        }  
        return strs[0];  
    }  
};