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# Subarrays with equal 1s and 0s

Given an array **arr\[]** of size **N** containing **0s** and **1s** only. The task is to count the subarrays having equal number of 0s and 1s.

**Input:**\
The first line of input contains an integer **T** denoting the number of test cases. Then **T** test cases follow. Each test case consists of two lines. First line of each test case contains an Integer **N** denoting size of array and the second line contains **N** space separated **0** and **1**.

**Output:**\
For each test case, print the count of required sub arrays in new line.

**Constraints:**\
1 <= T <= 100\
1 <= N <= 106\
0 <= A\[i] <= 1

**Example:**\
**Input:**\
2\
7\
1 0 0 1 0 1 1\
5\
1 1 1 1 0

**Output:**\
8\
1

**Explanation:**\
**Testcase 1:** The index range for the 8 sub-arrays are:\
(0, 1), (2, 3), (0, 3), (3, 4), (4, 5)\
(2, 5), (0, 5), (1, 6)

```java
class Solution {
    public static int numberOfSubarrays(int[] arr, int n) {
        // Turn zeros into -1
        for (int i = 0; i < n; i++)
            if (arr[i] == 0)
                arr[i] = -1;
        // Map of sum -> frequency
        Map<Integer, Integer> map = new HashMap<>();
        map.put(0, 1);
        int count = 0, sum = 0;
        for (int x : arr) {
            sum += x;
            if (map.containsKey(sum))
                count += map.get(sum);
            map.put(sum, map.getOrDefault(sum, 0) + 1);
        }
        return count;
    }
}
```