<p>Given an array of integers <code>arr</code>.</p>

<p>We want to select three indices <code>i</code>, <code>j</code> and <code>k</code> where <code>(0 &lt;= i &lt; j &lt;= k &lt; arr.length)</code>.</p>

<p>Let&#39;s define <code>a</code> and <code>b</code> as follows:</p>

<ul>
	<li><code>a = arr[i] ^ arr[i + 1] ^ ... ^ arr[j - 1]</code></li>
	<li><code>b = arr[j] ^ arr[j + 1] ^ ... ^ arr[k]</code></li>
</ul>

<p>Note that <strong>^</strong> denotes the <strong>bitwise-xor</strong> operation.</p>

<p>Return <em>the number of triplets</em> (<code>i</code>, <code>j</code> and <code>k</code>) Where <code>a == b</code>.</p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>

<pre>
<strong>Input:</strong> arr = [2,3,1,6,7]
<strong>Output:</strong> 4
<strong>Explanation:</strong> The triplets are (0,1,2), (0,2,2), (2,3,4) and (2,4,4)
</pre>

<p><strong class="example">Example 2:</strong></p>

<pre>
<strong>Input:</strong> arr = [1,1,1,1,1]
<strong>Output:</strong> 10
</pre>

<p>&nbsp;</p>
<p><strong>Constraints:</strong></p>

<ul>
	<li><code>1 &lt;= arr.length &lt;= 300</code></li>
	<li><code>1 &lt;= arr[i] &lt;= 10<sup>8</sup></code></li>
</ul>

class Solution:
    def countTriplets(self, arr: List[int]) -> int:
        # pick 3 indices, i < j < k from arr
        # a is subarr from i to j - 1
        # b is subarr from j to k
        # number of triplets so a = b
        # (i, j) is one bound and (j, k) is the other bound
        prefix_xor = [0] * len(arr)
        prefix_xor[0] = arr[0]
        n = len(arr)
        ct = 0
        for i in range(1, len(arr)):
            v = arr[i]
            prefix_xor[i] = prefix_xor[i - 1] ^ v
        # print(prefix_xor)
        for s in range(n):
            for e in range(s, n):
                subarr = arr[s:e + 1] # s is inclusive, e is not
                xor_val = prefix_xor[e] ^ prefix_xor[s - 1]
                if s == 0:
                    xor_val = prefix_xor[e]
                
                if xor_val == 0:
                    ct += e - s

                # print(subarr)
                # if s == 0:
                    # print(subarr)
                    # print(prefix_xor[e])
                    # print(s, e)
                # else:
                    # print(subarr)
                    # print(prefix_xor[e] ^ prefix_xor[s - 1])
                # print(subarr)
                # print(prefix_xor[e] ^ prefix_xor[s - 1])
                # if prefix_xor[e] ^ prefix_xor[s - 1] == 0:
                    # ct += (e - s - 1)

        # print(prefix_xor)
        return ct
99