Find the Longest Balanced Substring of a Binary String Python/Java solution

Python and Java solutions typically implement the count-balance technique. Iterate through the string, track consecutive 0 and 1 counts, and update the maximum with 2 * min(count0, count1). The algorithm runs in O(n) time and requires only constant extra space.

What is the best approach for Find the Longest Balanced Substring of a Binary String?

The best approach is the Count Balance method, which scans the string and counts consecutive groups of 0s and 1s. For each 0-block followed by a 1-block, compute 2 * min(count0, count1) and track the maximum length. This solution runs in O(n) time with O(1) space and directly matches the problem’s 0^k1^k structure.

Is Find the Longest Balanced Substring of a Binary String asked at Google/Amazon/Meta?

Balanced substring and binary pattern problems frequently appear in interviews at large tech companies such as Amazon, Google, and Meta. Variations often test string scanning, prefix sums, or two-pointer reasoning, making this problem a common practice question for entry-level coding interviews.

What data structure is used in Find the Longest Balanced Substring of a Binary String?

The optimal solution uses simple integer counters while scanning the string, so no additional data structures are required. Alternative implementations may use a hash map to store prefix sums when applying a prefix-sum-based strategy.

What is the time complexity of Find the Longest Balanced Substring of a Binary String?

The optimal solution runs in O(n) time because the binary string is scanned once while maintaining counts of consecutive characters. Space complexity can be O(1) using the count-balance approach or O(n) if a prefix sum map is used to store intermediate states.

Description Hints 2 Solution Video 5:10

2609. Find the Longest Balanced Substring of a Binary String

Q: Is Find the Longest Balanced Substring of a Binary String easy or hard?

LeetCode classifies this problem as Easy. The main challenge is recognizing that valid substrings must follow the strict pattern of consecutive 0s followed by the same number of 1s. Once that constraint is clear, a simple linear scan solves the problem efficiently.

Q: How to solve Find the Longest Balanced Substring of a Binary String in O(n)?

Iterate through the string and count consecutive 0s first. When 1s begin, count them as well and compute the candidate length as 2 * min(count0, count1). Update the maximum length while scanning. Reset counters when a new 0 sequence begins. This single-pass technique guarantees O(n) time complexity.

Easy46.6% acceptance1 company

You are given a binary string s consisting only of zeroes and ones.

A substring of s is considered balanced if all zeroes are before ones and the number of zeroes is equal to the number of ones inside the substring. Notice that the empty substring is considered a balanced substring.

Return the length of the longest balanced substring of s.

A substring is a contiguous sequence of characters within a string.

Example 1:

Input: s = "01000111"
Output: 6
Explanation: The longest balanced substring is "000111", which has length 6.

Example 2:

Input: s = "00111"
Output: 4
Explanation: The longest balanced substring is "0011", which has length 4.

Example 3:

Input: s = "111"
Output: 0
Explanation: There is no balanced substring except the empty substring, so the answer is 0.

Constraints:

1 <= s.length <= 50
'0' <= s[i] <= '1'

Asked at 1 company

Tinkoff

Topics

String

Hints open one at a time

Hint 1

Consider iterating over each subarray and checking if it’s balanced or not.

Hint 2

Among all balanced subarrays, the answer is the longest one of them.

5:10

Still stuck?Read 4 approaches, or watch a walkthrough.

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1class Solution:
2    def findTheLongestBalancedSubstring(self, s: str) -> int:
3        

Starter codePython 3Spaces: 4

Examples

Case 1Case 2Case 3

Input

"01000111"

Input

"00111"

Input

"111"

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