<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 Trie {
public:
    Trie* child[2];
    Trie() {
        for(int i = 0; i < 2; i++) {
            child[i] = NULL;
        }
    }
};

class Solution {
public:
    Trie* root = new Trie();

    void insert(string s) {
        Trie* temp = root;
        for (auto ch : s) {
            int ind = ch - '0';
            if (temp->child[ind] == NULL) {
                temp->child[ind] = new Trie();
            }
            temp = temp->child[ind];
        }
    }

    string bitcon(int x) {
        string ans = "";
        for (int i = 31; i >= 0; i--) {
            int bit = (x >> i) & 1;
            ans += to_string(bit);
        }
        return ans;
    }

    int findMaximumXOR(vector<int>& nums) {
        vector<string> bits;
        for (auto num : nums) {
            string st = bitcon(num);
            insert(st);
            bits.push_back(st);
        }

        int ansmax = 0;
        for (auto bit : bits) {
            int res = 0;
            Trie* temp = root;
            for (auto b : bit) {
                int ind = b - '0';
                int flip = 1 - ind;
                if (temp->child[flip] != NULL) {
                    res = (res << 1) | 1;
                    temp = temp->child[flip];
                } else {
                    res = res << 1;
                    temp = temp->child[ind];
                }
            }
            ansmax = max(ansmax, res);
        }

        return ansmax;
    }
};

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