Shortest String That Contains Three Strings
Given three strings <code>a</code>, <code>b</code>, and <code>c</code>, your task is to find a string that has the<strong> minimum</strong> length and contains all three strings as <strong>substrings</strong>.

<p>If there are multiple such strings, return the<em> </em><strong>lexicographically<em> </em>smallest </strong>one.</p>

<p>Return <em>a string denoting the answer to the problem.</em></p>

<p><strong>Notes</strong></p>

<ul>
	<li>A string <code>a</code> is <strong>lexicographically smaller</strong> than a string <code>b</code> (of the same length) if in the first position where <code>a</code> and <code>b</code> differ, string <code>a</code> has a letter that appears <strong>earlier </strong>in the alphabet than the corresponding letter in <code>b</code>.</li>
	<li>A <strong>substring</strong> is a contiguous sequence of characters within a string.</li>
</ul>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>

<pre>
<strong>Input:</strong> a = &quot;abc&quot;, b = &quot;bca&quot;, c = &quot;aaa&quot;
<strong>Output:</strong> &quot;aaabca&quot;
<strong>Explanation:</strong>  We show that &quot;aaabca&quot; contains all the given strings: a = ans[2...4], b = ans[3..5], c = ans[0..2]. It can be shown that the length of the resulting string would be at least 6 and &quot;aaabca&quot; is the lexicographically smallest one.</pre>

<p><strong class="example">Example 2:</strong></p>

<pre>
<strong>Input:</strong> a = &quot;ab&quot;, b = &quot;ba&quot;, c = &quot;aba&quot;
<strong>Output:</strong> &quot;aba&quot;
<strong>Explanation: </strong>We show that the string &quot;aba&quot; contains all the given strings: a = ans[0..1], b = ans[1..2], c = ans[0..2]. Since the length of c is 3, the length of the resulting string would be at least 3. It can be shown that &quot;aba&quot; is the lexicographically smallest one.
</pre>

<p>&nbsp;</p>
<p><strong>Constraints:</strong></p>

<ul>
	<li><code>1 &lt;= a.length, b.length, c.length &lt;= 100</code></li>
	<li><code>a</code>, <code>b</code>, <code>c</code> consist only of lowercase English letters.</li>
</ul>
Greedy; String; Enumeration
class Solution {
public:
    string minimumString(string a, string b, string c) {
        vector<string> s = {a, b, c};
        vector<vector<int>> perm = {{0, 1, 2}, {0, 2, 1}, {1, 0, 2}, {1, 2, 0}, {2, 1, 0}, {2, 0, 1}};
        string ans = "";
        for (auto& p : perm) {
            int i = p[0], j = p[1], k = p[2];
            string t = f(f(s[i], s[j]), s[k]);
            if (ans == "" || t.size() < ans.size() || (t.size() == ans.size() && t < ans)) {
                ans = t;
            }
        }
        return ans;
    }

    string f(string s, string t) {
        if (s.find(t) != string::npos) {
            return s;
        }
        if (t.find(s) != string::npos) {
            return t;
        }
        int m = s.size(), n = t.size();
        for (int i = min(m, n); i; --i) {
            if (s.substr(m - i) == t.substr(0, i)) {
                return s + t.substr(i);
            }
        }
        return s + t;
    };
};