<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 TrieNode{
    public:
    TrieNode* child[2];
    TrieNode() {
        child[0] = nullptr;
        child[1] = nullptr;
    }
};

class Solution {
public:
    int findMaximumXOR(vector<int>& nums) {
        TrieNode *root = new TrieNode;
        TrieNode* curr = root;
        for(int i = 0; i<nums.size(); i++) {
            insert(nums[i], curr);
        }
        int ans = 0;
        curr = root;
        for(int i = 0; i<nums.size(); i++) {
            findMax(nums[i], curr, ans);
        }
        return ans;
    }
private:
    void insert(int x, TrieNode* root) {
        vector<int> bn(32, 0);
        for(int i = 0; i<32; i++) {
            bn[i] = x%2;
            x/=2;
        }
        reverse(bn.begin(), bn.end());
        for(int i = 0; i<32; i++) {
            if(!root->child[bn[i]]) {
                root->child[bn[i]] = new TrieNode();
            }
            root = root->child[bn[i]];
        }
    }
    void findMax(int x, TrieNode* root, int& ans) {
        int res = 0;
        vector<int> bn(32, 0);
        for(int i = 0; i<32; i++) {
            bn[i] = x%2;
            x/=2;
        }
        reverse(bn.begin(), bn.end());
        for(int i = 0; i<32; i++) {
            if(!root->child[!bn[i]]) {
                root = root->child[bn[i]];
            }
            else {
                res += (1<<(31-i));
                root = root->child[!bn[i]];
            }
        }
        ans = max(res, ans);
    }
};
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