<p>There is an integer array <code>perm</code> that is a permutation of the first <code>n</code> positive integers, where <code>n</code> is always <strong>odd</strong>.</p>

<p>It was encoded into another integer array <code>encoded</code> of length <code>n - 1</code>, such that <code>encoded[i] = perm[i] XOR perm[i + 1]</code>. For example, if <code>perm = [1,3,2]</code>, then <code>encoded = [2,1]</code>.</p>

<p>Given the <code>encoded</code> array, return <em>the original array</em> <code>perm</code>. It is guaranteed that the answer exists and is unique.</p>

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

<pre>
<strong>Input:</strong> encoded = [3,1]
<strong>Output:</strong> [1,2,3]
<strong>Explanation:</strong> If perm = [1,2,3], then encoded = [1 XOR 2,2 XOR 3] = [3,1]
</pre>

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

<pre>
<strong>Input:</strong> encoded = [6,5,4,6]
<strong>Output:</strong> [2,4,1,5,3]
</pre>

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

<ul>
	<li><code>3 &lt;= n &lt;&nbsp;10<sup>5</sup></code></li>
	<li><code>n</code>&nbsp;is odd.</li>
	<li><code>encoded.length == n - 1</code></li>
</ul>

class Solution {
public:
    vector<int> decode(vector<int>& encoded) {
        const int n = encoded.size();
        int allxor = 0, allxor2 = 0;
        int c = 0;
        for (int i = n - 1; i >= 0; i--) {
            encoded[i] = c = encoded[i] ^ c;
            allxor ^= c;
            allxor2 ^= i + 1;
        }
        int num = allxor ^ allxor2 ^ (n + 1);

        for (int i = 0; i < n; i++)
            encoded[i] ^= num;
        encoded.push_back(num);
        return encoded;
    }
};
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