Largest Subarray of 0's and 1's

The problem. Given an array nums that contains only 0s and 1s, return the length of the longest subarray with as many 0s as 1s. If there is none, return 0. (On LeetCode this is *Contiguous Array*.)

The array 1, 0, 1, 1, 1, 0, 0. The subarray from index 1 to 6, which is 0, 1, 1, 1, 0, 0, has three 0s and three 1s: length 6, the longest.

Example

nums = [1, 0, 1, 1, 1, 0, 0]  ->  6    ([0, 1, 1, 1, 0, 0])
nums = [0, 0, 1, 1, 0]        ->  4    ([0, 0, 1, 1] or [0, 1, 1, 0])
nums = [1, 1, 1]              ->  0

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Still to come

1. Brute force: recount every subarray
2. Optimal: running counts for every start
The key idea: count a 0 as −1
3. Best solution: balance + the first index of each balance
Comparing the approaches
Edge cases to test
Variations

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Largest Subarray of 0's and 1's

Example

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