Find the Lexicographically Largest String From the Box II
<p>You are given a string <code>word</code>, and an integer <code>numFriends</code>.</p>

<p>Alice is organizing a game for her <code>numFriends</code> friends. There are multiple rounds in the game, where in each round:</p>

<ul>
	<li><code>word</code> is split into <code>numFriends</code> <strong>non-empty</strong> strings, such that no previous round has had the <strong>exact</strong> same split.</li>
	<li>All the split words are put into a box.</li>
</ul>

<p>Find the <strong>lexicographically largest</strong> string from the box after all the rounds are finished.</p>

<p>A string <code>a</code> is <strong>lexicographically smaller</strong> than a string <code>b</code> if in the first position where <code>a</code> and <code>b</code> differ, string <code>a</code> has a letter that appears earlier in the alphabet than the corresponding letter in <code>b</code>.<br />
If the first <code>min(a.length, b.length)</code> characters do not differ, then the shorter string is the lexicographically smaller one.</p>

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

<div class="example-block">
<p><strong>Input:</strong> <span class="example-io">word = &quot;dbca&quot;, numFriends = 2</span></p>

<p><strong>Output:</strong> <span class="example-io">&quot;dbc&quot;</span></p>

<p><strong>Explanation:</strong></p>

<p>All possible splits are:</p>

<ul>
	<li><code>&quot;d&quot;</code> and <code>&quot;bca&quot;</code>.</li>
	<li><code>&quot;db&quot;</code> and <code>&quot;ca&quot;</code>.</li>
	<li><code>&quot;dbc&quot;</code> and <code>&quot;a&quot;</code>.</li>
</ul>
</div>

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

<div class="example-block">
<p><strong>Input:</strong> <span class="example-io">word = &quot;gggg&quot;, numFriends = 4</span></p>

<p><strong>Output:</strong> <span class="example-io">&quot;g&quot;</span></p>

<p><strong>Explanation:</strong></p>

<p>The only possible split is: <code>&quot;g&quot;</code>, <code>&quot;g&quot;</code>, <code>&quot;g&quot;</code>, and <code>&quot;g&quot;</code>.</p>
</div>

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

<ul>
	<li><code>1 &lt;= word.length &lt;= 2 * 10<sup>5</sup></code></li>
	<li><code>word</code> consists only of lowercase English letters.</li>
	<li><code>1 &lt;= numFriends &lt;= word.length</code></li>
</ul>
Two Pointers; String
class Solution {
public:
    string answerString(string word, int numFriends) {
        if (numFriends == 1) {
            return word;
        }
        string s = lastSubstring(word);
        return s.substr(0, min(s.length(), word.length() - numFriends + 1));
    }

    string lastSubstring(string& s) {
        int n = s.size();
        int i = 0, j = 1, k = 0;
        while (j + k < n) {
            if (s[i + k] == s[j + k]) {
                ++k;
            } else if (s[i + k] < s[j + k]) {
                i += k + 1;
                k = 0;
                if (i >= j) {
                    j = i + 1;
                }
            } else {
                j += k + 1;
                k = 0;
            }
        }
        return s.substr(i);
    }
};