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class Solution {
public:
    bool EqualAll(vector<string>& strs, int k) {
        for(int i = 1; i < strs.size(); i++) {
            if(strs[i][k] != strs[0][k]) return false;
        }
        return true;
    }
    string longestCommonPrefix(vector<string>& strs) {
        string ans = "";
        if(strs.size() <= 0) return ans;
        int len = 0xffff;
        for(int i = 0; i < strs.size(); i++) {
            if(strs[i].size() < len) len = strs[i].size();
        }
        for(int i = 0; i < len; i++) {
            if(EqualAll(strs, i))
                ans.push_back(strs[0][i]);
            else
                return ans;
        }
        return ans;
    }
};