Example 1
Input
longest_equal_subarray([0, 1, 0, 1, 1, 0])
Output
6
The whole array has three 0s and three 1s, so length is 6.
Full lesson preview
Find the longest subarray with equal 0s and 1s
Given a binary array, return the length of the longest contiguous subarray with equal numbers of 0s and 1s.
Python practice28 minHashing & SetsAdvancedLast updated March 26, 2026
Problem statement
Given an array containing only 0s and 1s, find the length of the longest contiguous subarray that contains an equal number of 0s and 1s. Convert 0s to -1s and track prefix sums; the longest distance between identical prefix sums indicates a balanced subarray.
Task
Use prefix sums and hashing to detect subarrays with equal counts efficiently (O(n) time, O(n) space).
Examples
Input format
A list of integers containing only 0 and 1
Output format
An integer representing the maximum length of a contiguous subarray with equal 0s and 1s
Constraints
0 <= len(arr) <= 10^5; arr[i] in {0,1}; target O(n) time using hashmap of prefix sums
Samples
Sample 1
Input
[0,1,0,1,1,0]
Output
6
Full array balances to length 6