> For the complete documentation index, see [llms.txt](https://mayanktyagi3111.gitbook.io/interview-prep/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://mayanktyagi3111.gitbook.io/interview-prep/hashmap-and-hashset-and-sliding-window/untitled-5.md).

# Contiguous Array

Given a binary array, find the maximum length of a contiguous subarray with equal number of 0 and 1.

**Example 1:**<br>

```
Input: [0,1]
Output: 2
Explanation: [0, 1] is the longest contiguous subarray with equal number of 0 and 1.
```

**Example 2:**<br>

```
Input: [0,1,0]
Output: 2
Explanation: [0, 1] (or [1, 0]) is a longest contiguous subarray with equal number of 0 and 1.
```

**Note:** The length of the given binary array will not exceed 50,000.

```java
/**
 * The idea is to change 0 in the original array to -1. Thus, if we find
 * SUM[i,j] == 0 then we know there are equal number of -1 and 1 between index i
 * and j. Also put the sum to index mapping to a HashMap to make search faster.
 */
public class Solution {
    public int findMaxLength(int[] nums) {
        for (int i = 0; i < nums.length; i++)
            if (nums[i] == 0)
                nums[i] = -1;
        // Map of sum -> index
        Map<Integer, Integer> sumToIndex = new HashMap<>();
        sumToIndex.put(0, -1);
        int sum = 0, max = 0;

        for (int i = 0; i < nums.length; i++) {
            sum += nums[i];
            if (sumToIndex.containsKey(sum))
                max = Math.max(max, i - sumToIndex.get(sum));
            else
                sumToIndex.put(sum, i);
        }

        return max;
    }
}
```


---

# Agent Instructions
This documentation is published with GitBook. GitBook is the documentation platform designed so that both humans and AI agents can read, navigate, and reason over technical content effectively. Learn more at gitbook.com.

## Querying This Documentation
If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter:

```
GET https://mayanktyagi3111.gitbook.io/interview-prep/hashmap-and-hashset-and-sliding-window/untitled-5.md?ask=<question>
```

The question should be specific, self-contained, and written in natural language.
The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.