README.md

2564. Substring XOR Queries

You are given a binary string s, and a 2D integer array queries where queries[i] = [firsti, secondi].

For the ith query, find the shortest substring of s whose decimal value, val, yields secondi when bitwise XORed with firsti. In other words, val ^ firsti == secondi.

The answer to the ith query is the endpoints (0-indexed) of the substring [lefti, righti] or [-1, -1] if no such substring exists. If there are multiple answers, choose the one with the minimum lefti.

Return an array ans where ans[i] = [lefti, righti] is the answer to the ith query.

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

Example 1:

Input: s = "101101", queries = [[0,5],[1,2]]
Output: [[0,2],[2,3]]
Explanation: For the first query the substring in range [0,2] is "101" which has a decimal value of 5, and 5 ^ 0 = 5, hence the answer to the first query is [0,2]. In the second query, the substring in range [2,3] is "11", and has a decimal value of 3, and 3 ^ 1 = 2. So, [2,3] is returned for the second query.

Example 2:

Input: s = "0101", queries = [[12,8]]
Output: [[-1,-1]]
Explanation: In this example there is no substring that answers the query, hence [-1,-1] is returned.

Example 3:

Input: s = "1", queries = [[4,5]]
Output: [[0,0]]
Explanation: For this example, the substring in range [0,0] has a decimal value of 1, and 1 ^ 4 = 5. So, the answer is [0,0].

Constraints:

• 1 <= s.length <= 104
• s[i] is either '0' or '1'.
• 1 <= queries.length <= 105
• 0 <= firsti, secondi <= 109

Solutions (Python)

1. Solution

class Solution:
    def substringXorQueries(self, s: str, queries: List[List[int]]) -> List[List[int]]:
        vals = {}

        for i in range(len(s)):
            if s[i] == '0':
                if 0 not in vals:
                    vals[0] = [i, i]
                continue

            val = 0

            for j in range(i, min(len(s), i + 32)):
                val = (val << 1) + int(s[j])
                if val not in vals:
                    vals[val] = [i, j]

        return [vals.get(first ^ second, [-1, -1]) for first, second in queries]