Palindrome Rearrangement Queries — LeetCode 2983 Python Solution

HardHash TableStringPrefix Sum
Problem
#2983
Pattern
Prefix Sum
Reading time
10 min

The problem

You are given a 0-indexed string s having an even length n. You are also given a 0-indexed 2D integer array, queries, where queries[i] = [ai, bi, ci, di].

Example

Input
s = "abcabc", queries = [[1,1,3,5],[0,2,5,5]]
Output
[true,true]
Explanation
In this example, there are two queries:

Python solution

Python
class Solution:
    def canMakePalindromeQueries(self, s: str, queries: List[List[int]]) -> List[bool]:
        def count(pre: List[List[int]], i: int, j: int) -> List[int]:
            return [x - y for x, y in zip(pre[j + 1], pre[i])]

        def sub(cnt1: List[int], cnt2: List[int]) -> List[int]:
            res = []
            for x, y in zip(cnt1, cnt2):
                if x - y < 0:
                    return []
                res.append(x - y)
            return res

        def check(
            pre1: List[List[int]], pre2: List[List[int]], a: int, b: int, c: int, d: int
        ) -> bool:
            if diff[a] > 0 or diff[m] - diff[max(b, d) + 1] > 0:
                return False
            if d <= b:
                return count(pre1, a, b) == count(pre2, a, b)
            if b < c:
                return (
                    diff[c] - diff[b + 1] == 0
                    and count(pre1, a, b) == count(pre2, a, b)
                    and count(pre1, c, d) == count(pre2, c, d)
                )
            cnt1 = sub(count(pre1, a, b), count(pre2, a, c - 1))
            cnt2 = sub(count(pre2, c, d), count(pre1, b + 1, d))
            return bool(cnt1) and bool(cnt2) and cnt1 == cnt2

        n = len(s)
        m = n // 2
        t = s[m:][::-1]
        s = s[:m]
        pre1 = [[0] * 26 for _ in range(m + 1)]
        pre2 = [[0] * 26 for _ in range(m + 1)]
        diff = [0] * (m + 1)
        for i, (c1, c2) in enumerate(zip(s, t), 1):
            pre1[i] = pre1[i - 1][:]
            pre2[i] = pre2[i - 1][:]
            pre1[i][ord(c1) - ord("a")] += 1
            pre2[i][ord(c2) - ord("a")] += 1
            diff[i] = diff[i - 1] + int(c1 != c2)
        ans = []
        for a, b, c, d in queries:
            c, d = n - 1 - d, n - 1 - c
            ok = (
                check(pre1, pre2, a, b, c, d)
                if a <= c
                else check(pre2, pre1, c, d, a, b)
            )
            ans.append(ok)
        return ans

Complexity

MeasureComplexity
TimeO((n + q) \times |\Sigma|)
SpaceO(n \times |\Sigma|) auxiliary

Pattern: Prefix Sum

Precompute running totals once so any range query becomes a single subtraction. LeetCode 2983. Palindrome Rearrangement Queries is filed here because LeetCode tags it Prefix Sum, which is the vocabulary this hub collects.

The prefix sum guide has the Python template for the pattern and the 157 LeetCode problems that use it.

Related problems

Frequently asked questions

How hard is LeetCode 2983. Palindrome Rearrangement Queries?
LeetCode 2983. Palindrome Rearrangement Queries is rated Hard on LeetCode.
What is the time complexity of LeetCode 2983. Palindrome Rearrangement Queries?
The Python solution on this page runs in O((n + q) \times |\Sigma|).
What is the space complexity of LeetCode 2983. Palindrome Rearrangement Queries?
The Python solution on this page uses O(n \times |\Sigma|) auxiliary space.
What topics does LeetCode 2983. Palindrome Rearrangement Queries cover?
LeetCode 2983. Palindrome Rearrangement Queries is tagged Hash Table, String and Prefix Sum on LeetCode.

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