Formatted question description: https://leetcode.ca/all/1593.html
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
-
s
contains only lower case English letters.
Related Topics:
Backtracking
Solution 1. Backtrack
// OJ: https://leetcode.com/problems/split-a-string-into-the-max-number-of-unique-substrings/
// Time: O(2^N)
// Space: O(N)
class Solution {
unordered_set<string> m;
int ans = 0;
void dfs(string &s, int i) {
if (i == s.size()) {
ans = max(ans, (int)m.size());
return;
}
for (int j = i; j < s.size(); ++j) {
string sub = s.substr(i, j - i + 1);
if (m.count(sub)) continue;
m.insert(sub);
dfs(s, j + 1);
m.erase(sub);
}
}
public:
int maxUniqueSplit(string s) {
dfs(s, 0);
return ans;
}
};
Java
class Solution {
public int maxUniqueSplit(String s) {
int length = s.length();
if (length == 1)
return 1;
int maxSplit = 1;
int total = 1 << (length - 1);
for (int i = 1; i < total; i++) {
boolean[] split = new boolean[length - 1];
int mask = i;
int splitCount = 1;
for (int j = 0; j < length - 1 && mask > 0; j++) {
if (mask % 2 == 1) {
split[j] = true;
splitCount++;
}
mask /= 2;
}
if (splitCount > maxSplit && checkUnique(s, split, splitCount))
maxSplit = splitCount;
}
return maxSplit;
}
public boolean checkUnique(String s, boolean[] split, int splitCount) {
Set<String> set = new HashSet<String>();
int start = 0;
int length = s.length();
for (int i = 0; i < length - 1; i++) {
if (split[i]) {
set.add(s.substring(start, i + 1));
start = i + 1;
}
}
if (start < length)
set.add(s.substring(start));
return set.size() == splitCount;
}
}