java: add «1593. Split a String Into the Max Number of Unique Substrings»

URL:	https://leetcode.com/problems/split-a-string-into-the-max-number-of-unique-substrings/
Signed-off-by: Matej Focko <me@mfocko.xyz>

java/split-a-string-into-the-max-number-of-unique-substrings.java

@@ -0,0 +1,36 @@
+class Solution {
+  private Set<String> seen;
+  private int maxCount;
+
+  private void backtrack(String s, int start, int count) {
+    if (count + (s.length() - start) <= maxCount) {
+      return;
+    }
+
+    if (start == s.length()) {
+      maxCount = Math.max(maxCount, count);
+      return;
+    }
+
+    for (int end = start + 1; end <= s.length(); ++end) {
+      var sub = s.substring(start, end);
+      if (seen.contains(sub)) {
+        continue;
+      }
+
+      seen.add(sub);
+      backtrack(s, end, count + 1);
+      seen.remove(sub);
+    }
+  }
+
+  public int maxUniqueSplit(String s) {
+    seen = new HashSet<>();
+    maxCount = 0;
+
+    backtrack(s, 0, 0);
+
+    seen = null;
+    return maxCount;
+  }
+}