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3365. Rearrange K Substrings to Form Target String

Description

You are given two strings s and t, both of which are anagrams of each other, and an integer k.

Your task is to determine whether it is possible to split the string s into k equal-sized substrings, rearrange the substrings, and concatenate them in any order to create a new string that matches the given string t.

Return true if this is possible, otherwise, return false.

An anagram is a word or phrase formed by rearranging the letters of a different word or phrase, using all the original letters exactly once.

A substring is a contiguous non-empty sequence of characters within a string.

 

Example 1:

Input: s = "abcd", t = "cdab", k = 2

Output: true

Explanation:

  • Split s into 2 substrings of length 2: ["ab", "cd"].
  • Rearranging these substrings as ["cd", "ab"], and then concatenating them results in "cdab", which matches t.

Example 2:

Input: s = "aabbcc", t = "bbaacc", k = 3

Output: true

Explanation:

  • Split s into 3 substrings of length 2: ["aa", "bb", "cc"].
  • Rearranging these substrings as ["bb", "aa", "cc"], and then concatenating them results in "bbaacc", which matches t.

Example 3:

Input: s = "aabbcc", t = "bbaacc", k = 2

Output: false

Explanation:

  • Split s into 2 substrings of length 3: ["aab", "bcc"].
  • These substrings cannot be rearranged to form t = "bbaacc", so the output is false.

 

Constraints:

  • 1 <= s.length == t.length <= 2 * 105
  • 1 <= k <= s.length
  • s.length is divisible by k.
  • s and t consist only of lowercase English letters.
  • The input is generated such that s and t are anagrams of each other.

Solutions

Solution 1: Hash Table

Let the length of the string $s$ be $n$, then the length of each substring is $m = n / k$.

We use a hash table $\textit{cnt}$ to record the difference between the number of occurrences of each substring of length $m$ in string $s$ and in string $t$.

We traverse the string $s$, extracting substrings of length $m$ each time, and update the hash table $\textit{cnt}$.

Finally, we check whether all values in the hash table $\textit{cnt}$ are $0$.

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

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class Solution:
    def isPossibleToRearrange(self, s: str, t: str, k: int) -> bool:
        cnt = Counter()
        n = len(s)
        m = n // k
        for i in range(0, n, m):
            cnt[s[i : i + m]] += 1
            cnt[t[i : i + m]] -= 1
        return all(v == 0 for v in cnt.values())

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class Solution {
    public boolean isPossibleToRearrange(String s, String t, int k) {
        Map<String,