2800-shortest-string-that-contains-three-strings.cs

public class Solution {
    public string MinimumString(string a, string b, string c) {
        string merge(string s1, string s2) {
            if (s1.Contains(s2)) return s1;
            for (int i = 0; i < s1.Length; i++) {
                if (s2.StartsWith(s1.Substring(i))) return s1.Substring(0, i) + s2;
            }
            return s1 + s2;
        }

        string res = "";
        int l = int.MaxValue;
        foreach (string s in new string[] {
            merge(merge(a, b), c),
            merge(merge(b, a), c),
            merge(merge(c, b), a),
            merge(merge(b, c), a),
            merge(merge(a, c), b),
            merge(merge(c, a), b)
        }) {
            if (s.Length < l) {
                res = s;
                l = s.Length;
            } else if (s.Length == l) {
                res = string.CompareOrdinal(res, s) < 0 ? res : s;
            }
        }

        return res;
    }
}