<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 {
public:
    class TrieNode {
        public:
        TrieNode* one;
        TrieNode* zero;
        TrieNode() {
            one = NULL;
            zero = NULL;
        }
    };

    TrieNode *root;
    void insert(string &s) {
        TrieNode* cur = root;
        for (auto x: s) {
            if (x == '0') {
                if (cur->zero == NULL) cur->zero = new TrieNode();
                cur = cur->zero;
            }
            else {
                if (cur->one == NULL) cur->one = new TrieNode();
                cur = cur->one;
            }
        }
    }

    int getVal(string &s) {
        TrieNode* cur = root;
        int val = 0, i = 30;
        for (auto x: s) {
            if (x == '0') {
                if (cur->one != NULL) {
                    cur = cur->one;
                    val += (1 << i);
                }
                else {
                    cur = cur->zero;
                }
            }
            else {
                if (cur->zero != NULL) {
                    cur = cur->zero;
                    val += (1 << i);
                }
                else {
                    cur = cur->one;
                }
            }
            i--;
        }
        return val;
    }

    int findMaximumXOR(vector<int>& a) {
        root = new TrieNode();
        unordered_map<int, string> bin;
        for (auto x: a) {
            string s = "";
            for (int i = 30; i >= 0; i--) {
                if (x & (1 << i)) s.push_back('1');
                else s.push_back('0');
            }
            bin[x] = s;
            insert(s);
        }

        int ans = 0;

        for (auto x: a) {
            ans = max(ans, getVal(bin[x]));
        }

        return ans;
    }
};
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