14. Longest Common Prefix

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

思路：两个循环必不可少

    public String longestCommonPrefix(String[] strs) {
        String commonStr = "";
        if (strs.length==0){
            return commonStr;
        }

        commonStr = strs[0];
        for (int i=1;i<strs.length;i++){
            commonStr = CommonPrefix(commonStr,strs[i]);
        }

        return commonStr;
    }

    public String CommonPrefix(String str1, String str2){
        StringBuilder commonStr = new StringBuilder();
        int i = 0;
        while(i<str1.length()&&i<str2.length()&&str1.charAt(i)==str2.charAt(i)){
            commonStr.append(str1.charAt(i));
            i++;
        }
        return commonStr.toString();
    }
}

C++ code

class Solution {
public:
    string longestCommonPrefix(vector<string>& strs) {
        if (strs.size()==0) return "";

        string commonPre = strs[0];
        for (int i=1;i<strs.size();i++){
            commonPre = getCommon(commonPre,strs[i]);
        }

        return commonPre;
    }

    string getCommon(string str1, string str2){
        string newCommon = "";
        int len = min(str1.size(),str2.size());
        for(int i=0; i<len && str1[i]==str2[i]; i++){
            newCommon += str1[i];
        }
        return newCommon;
    }
};