<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:
//for explaination see first comment in first solution
    int findMaximumXOR(vector<int>& nums) {
         int ans=0,mask=0;
         for(int i=31;i>=0;i--)
         {
             mask|=(1<<i);
             int desire=ans|(1<<i);
             unordered_set<int>s;
             for(auto &p:nums)
             {
                 int prefixpart=p&mask;
                 if(s.find(desire^prefixpart)!=s.end())
                 {
                     ans=desire;
                     break;
                 }
                 s.insert(prefixpart);
             }
         }
         return ans;
    }
};
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