[LeetCode] Longest Common Prefix

Problem Statement (link):
Write a function to find the longest common prefix string amongst an array of strings.
Analysis:
Pretty straight-forward. Choose any string, and compare its prefix - with length from 1 to the string length - with all other strings.

The time complexity is O(k*n), where k is the length of the string we choose, and n is the number of strings.

Code:

class Solution {
public:
    string longestCommonPrefix(vector<string> &strs) {
        int size = strs.size();
        string result = "";
        if (size==0) return result;
        if (size==1) return strs.front();
        if (strs[0].empty()) return result;
       
        int len = strs[0].length();    // The longest prefix cannot be longer than any string, so take 1st string
        for (int k = 1; k <= len; k++) {     // k - length of current prefix
            string pref = strs[0].substr(0, k);
            for (int i = 1; i < size; i++) {// check thru all the strings in the vector, i - current string
                if (strs[i].empty()) return result;
                string pref_curr = strs[i].substr(0, k);
                if (pref.compare(pref_curr) != 0)   return pref.substr(0, k-1);
                if (k==len && i==size-1) return pref;
            }
        }
    }
};