Is Count Binary Substrings easy or hard?

Count Binary Substrings is classified as an Easy problem on LeetCode with an acceptance rate above 70%. The challenge lies in recognizing that valid substrings occur only between adjacent groups of consecutive 0s and 1s, which leads to an efficient linear-time solution.

How to solve Count Binary Substrings in O(n)?

Traverse the string while counting lengths of consecutive characters. Maintain two values: the length of the previous group and the current group. Each time the current group length becomes less than or equal to the previous group, increment the answer. This guarantees all valid balanced substrings are counted in one linear pass.

What is the best approach for Count Binary Substrings?

The two-pointer group tracking approach is the most efficient. It scans the string once while keeping track of the current and previous group lengths of consecutive characters. Whenever the previous group is at least as large as the current one, a valid substring exists. This solution runs in O(n) time with O(1) space.

What data structure is used in Count Binary Substrings?

The problem mainly relies on string traversal and simple counters rather than complex data structures. Some implementations store group counts in an array or list, while the optimal approach only keeps two integer counters representing consecutive character groups.

What is the time complexity of Count Binary Substrings?

The optimal solution runs in O(n) time because the string is scanned once from left to right. Each character contributes to updating group lengths and possibly counting a substring. Space complexity can be O(1) using the two-pointer group tracking method or O(n) if a group count array is stored.

Count Binary Substrings Python or Java solution approach?

Both Python and Java solutions typically implement the two-pointer group tracking technique. Iterate through the string, track the current run length of identical characters, and compare it with the previous run length to count valid substrings. The algorithm runs in O(n) time and uses O(1) extra space.

Is Count Binary Substrings asked at Google, Amazon, or Meta?

Count Binary Substrings is a common easy-level interview problem that appears in coding screens and practice sets used by companies like Amazon, Google, and Meta. It tests pattern recognition in strings and the ability to reduce space complexity while maintaining linear time performance.

Description Hints 1 Solution Video 7:28

696. Count Binary Substrings

Easy70.3% acceptance18 companies

Given a binary string s, return the number of non-empty substrings that have the same number of 0's and 1's, and all the 0's and all the 1's in these substrings are grouped consecutively.

Substrings that occur multiple times are counted the number of times they occur.

Example 1:

Input: s = "00110011"
Output: 6
Explanation: There are 6 substrings that have equal number of consecutive 1's and 0's: "0011", "01", "1100", "10", "0011", and "01".
Notice that some of these substrings repeat and are counted the number of times they occur.
Also, "00110011" is not a valid substring because all the 0's (and 1's) are not grouped together.

Example 2:

Input: s = "10101"
Output: 4
Explanation: There are 4 substrings: "10", "01", "10", "01" that have equal number of consecutive 1's and 0's.

Constraints:

1 <= s.length <= 10⁵
s[i] is either '0' or '1'.

Asked at 18 companies

JPMorgan Chase Dell Helix Wells Fargo Blue Origin

IBM WeRide Meesho Amazon Microsoft Bloomberg Oracle

+6 more

D. E. Shaw Meta Uber Tiktok Salesforce

Google

Topics

String Two Pointers

Hints open one at a time

Hint 1

How many valid binary substrings exist in "000111", and how many in "11100"? What about "00011100"?

7:28

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