421. Maximum XOR of Two Numbers in an Array

Difficulty: Medium
29 / 29 test cases passed.
Runtime: 188 ms
Memory Usage: 18 MB

Author: YuriSpiridonov

Medium/421.MaximumXORofTwoNumbersinanArray.py

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+"""
+    Given a non-empty array of numbers, a0, a1, a2, … , an-1, where 0 ≤ ai < 231.
+    Find the maximum result of ai XOR aj, where 0 ≤ i, j < n.
+    Could you do this in O(n) runtime?
+
+    Example:
+    Input: [3, 10, 5, 25, 2, 8]
+    Output: 28
+    Explanation: The maximum result is 5 ^ 25 = 28.
+"""
+#Difficulty: Medium
+#29 / 29 test cases passed.
+#Runtime: 188 ms
+#Memory Usage: 18 MB
+
+#Runtime: 188 ms, faster than 72.25% of Python3 online submissions for Maximum XOR of Two Numbers in an Array.
+#Memory Usage: 18 MB, less than 89.19% of Python3 online submissions for Maximum XOR of Two Numbers in an Array.
+
+class Solution:
+    def findMaximumXOR(self, nums: List[int]) -> int:
+        maximum = 0
+        mask = 0
+        result = set()
+        length = len(nums)
+        for i in range(30, -1, -1):
+            mask |= 1 << i
+            new = maximum | 1 << i
+            for i in range(length):
+                result.add(nums[i] & mask)
+            for prefix in result:
+                if new ^ prefix  in result:
+                    maximum = new
+                    break
+            result.clear()
+        return maximum