LeetCode-in-Java
1593. Split a String Into the Max Number of Unique Substrings
Medium
Given a string s, return the maximum number of unique substrings that the given string can be split into.
You can split string s into any list of non-empty substrings, where the concatenation of the substrings forms the original string. However, you must split the substrings such that all of them are unique.
A substring is a contiguous sequence of characters within a string.
Example 1:
Input: s = “ababccc”
Output: 5
Explanation: One way to split maximally is [‘a’, ‘b’, ‘ab’, ‘c’, ‘cc’]. Splitting like [‘a’, ‘b’, ‘a’, ‘b’, ‘c’, ‘cc’] is not valid as you have ‘a’ and ‘b’ multiple times.
Example 2:
Input: s = “aba”
Output: 2
Explanation: One way to split maximally is [‘a’, ‘ba’].
Example 3:
Input: s = “aa”
Output: 1
Explanation: It is impossible to split the string any further.
Constraints:
-
1 <= s.length <= 16 -
scontains only lower case English letters.
Solution
import java.util.HashSet;
import java.util.Set;
public class Solution {
public int maxUniqueSplit(String s) {
int lo = 1;
int hi = s.length();
// binary search
while (lo < hi) {
int mid = (lo + hi + 1) >> 1;
if (ok(0, mid, 0, s, new HashSet<>())) {
lo = mid;
} else {
hi = mid - 1;
}
}
return lo;
}
private boolean ok(int depth, int end, int curLen, String s, Set<String> seen) {
if (depth == end) {
return true;
}
for (int j = curLen; j < s.length(); j++) {
// not enough length remains to reach the end.
if (s.length() - j < end - depth) {
break;
}
String cur = s.substring(curLen, j + 1);
if (seen.add(cur)) {
if (ok(depth + 1, end, j + 1, s, seen)) {
return true;
}
seen.remove(cur);
}
}
return false;
}
}