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2405. Optimal Partition of String

Description

Given a string s, partition the string into one or more substrings such that the characters in each substring are unique. That is, no letter appears in a single substring more than once.

Return the minimum number of substrings in such a partition.

Note that each character should belong to exactly one substring in a partition.

 

Example 1:

Input: s = "abacaba"
Output: 4
Explanation:
Two possible partitions are ("a","ba","cab","a") and ("ab","a","ca","ba").
It can be shown that 4 is the minimum number of substrings needed.

Example 2:

Input: s = "ssssss"
Output: 6
Explanation:
The only valid partition is ("s","s","s","s","s","s").

 

Constraints:

  • 1 <= s.length <= 105
  • s consists of only English lowercase letters.

Solutions

Solution 1: Greedy

According to the problem, each substring should be as long as possible and contain unique characters. We just need to partition greedily.

During the process, we can use a hash table to record all characters in the current substring, with a space complexity of $O(n)$; or we can use a number to record characters using bitwise operations, with a space complexity of $O(1)$.

The time complexity is $O(n)$, where $n$ is the length of the string $s$.

  • class Solution {
    public int partitionString(String s) {
        Set<Character> ss = new HashSet<>();
        int ans = 1;
        for (char c : s.toCharArray()) {
            if (ss.contains(c)) {
                ++ans;
                ss.clear();
            }
            ss.add(c);
        }
        return ans;
    }
}

  • class Solution {
public:
    int partitionString(string s) {
        unordered_set<char> ss;
        int ans = 1;
        for (char c : s) {
            if (ss.count(c)) {
                ++ans;
                ss.clear();
            }
            ss.insert(c);
        }
        return ans;
    }
};

  • class Solution:
    def partitionString(self, s: str) -> int:
        ss = set()
        ans = 1
        for c in s:
            if c in ss:
                ans += 1
                ss = set()
            ss.add(c)
        return ans


  • func partitionString(s string) int {
	ss := map[rune]bool{}
	ans := 1
	for _, c := range s {
		if ss[c] {
			ans++
			ss = map[rune]bool{}
		}
		ss[c] = true
	}
	return ans
}

  • function partitionString(s: string): number {
    const set = new Set();
    let res = 1;
    for (const c of s) {
        if (set.has(c)) {
            res++;
            set.clear();
        }
        set.add(c);
    }
    return res;
}


  • use std::collections::HashSet;
impl Solution {
    pub fn partition_string(s: String) -> i32 {
        let mut set = HashSet::new();
        let mut res = 1;
        for c in s.as_bytes().iter() {
            if set.contains(c) {
                res += 1;
                set.clear();
            }
            set.insert(c);
        }
        res
    }
}

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