14 Longest Common Prefix

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

Solution

class Solution {
public:
    string helper(string s1, string s2) {
        string s = "";
        int n1 = s1.size(), n2 = s2.size();
        if ( n1 == 0 or n2 == 0 ) return s;
        for ( int i = 0; i <= min(n1, n2)-1; i++ ){
            if ( s1[i] == s2[i] ) s += s1[i];
            else return s;
        }
        return s;
    }
    string longestCommonPrefix(vector<string>& strs) {
        int n = strs.size();
        string s = "";
        if ( n == 0 ) return s;
        s = strs[0];
        for ( int i = 1; i <= n-1; i++ ) s = helper(s, strs[i]);
        return s;
    }
};