<p>Given an integer array <code>nums</code>, return <em>the maximum result of </em><code>nums[i] XOR nums[j]</code>, where <code>0 &lt;= i &lt;= j &lt; n</code>.</p>

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

<pre>
<strong>Input:</strong> nums = [3,10,5,25,2,8]
<strong>Output:</strong> 28
<strong>Explanation:</strong> The maximum result is 5 XOR 25 = 28.
</pre>

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

<pre>
<strong>Input:</strong> nums = [14,70,53,83,49,91,36,80,92,51,66,70]
<strong>Output:</strong> 127
</pre>

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

<ul>
	<li><code>1 &lt;= nums.length &lt;= 2 * 10<sup>5</sup></code></li>
	<li><code>0 &lt;= nums[i] &lt;= 2<sup>31</sup> - 1</code></li>
</ul>

class Solution {
private:
    class Node {
     public:
        Node() {
            children[0] = nullptr;
            children[1] = nullptr;
        }
        Node* children[2];
    };
public:
    int findMaximumXOR(vector<int>& nums) {
        Node * root = new Node();
        int largest = 0;
        for (int num : nums) {
            if (num > largest) {
                largest = num;
            }
        }
        int scale = 0;
        while (largest > 0) {
            scale += 1;
            largest >>= 1;
        }
        if (scale < 1) {
            return 0;
        }
        for (int num : nums) {
            int mask = 1 << (scale -1);
            Node* p = root;
            while (mask > 0) {
                int bit = (mask & num) > 0 ? 1 : 0;
                if (p->children[bit] == nullptr) {
                    Node* r = new Node();
                    p->children[bit] = r;
                    p = r;
                } else {
                    p = p->children[bit];
                }
                mask >>= 1;
            }
        }
        int result = -1;
        for (int num : nums) {
            int mask = 1 << (scale -1);
            Node* p = root;
            int comp = 0;
            while (mask > 0) {
                int bit = (mask & num) > 0 ? 0 : 1;
                if (p->children[bit] == nullptr) {
                    bit = 1-bit;
                }
                comp |= bit * mask;
                p = p->children[bit];
                mask >>= 1;
            }
            if ((num^comp) > result) {
                result = num ^ comp;
            }
        }
        std::stack<Node*> cleanup;
        cleanup.push(root);
        while (!cleanup.empty()) {
            auto* node = cleanup.top();
            cleanup.pop();
            if (node->children[0] != nullptr) {
                cleanup.push(node->children[0]);
                node->children[0] = nullptr;
            }
            if (node->children[1] != nullptr) {
                cleanup.push(node->children[1]);
                node->children[1] = nullptr;
            }
            delete node;
        }
        return result;
    }
};
195531