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Maximum_XOR_of_Two_Numbers_in_an_Array.cpp
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Maximum_XOR_of_Two_Numbers_in_an_Array.cpp
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// Trie solution TLE !! The world is becomming more brutal
public class Solution {
class Trie {
Trie[] children;
public Trie() {
children = new Trie[2];
}
}
public int findMaximumXOR(int[] nums) {
if(nums == null || nums.length == 0) {
return 0;
}
// Init Trie.
Trie root = new Trie();
for(int num: nums) {
Trie curNode = root;
for(int i = 31; i >= 0; i --) {
int curBit = (num >>> i) & 1;
if(curNode.children[curBit] == null) {
curNode.children[curBit] = new Trie();
}
curNode = curNode.children[curBit];
}
}
int max = Integer.MIN_VALUE;
for(int num: nums) {
Trie curNode = root;
int curSum = 0;
for(int i = 31; i >= 0; i --) {
int curBit = (num >>> i) & 1;
if(curNode.children[curBit ^ 1] != null) {
curSum += (1 << i);
curNode = curNode.children[curBit ^ 1];
}else {
curNode = curNode.children[curBit];
}
}
max = Math.max(curSum, max);
}
return max;
}
}
// AC O(nlog k)
class Solution {
public:
int findMaximumXOR(vector<int>& nums) {
int n = nums.size();
int result = 0;
if(n < 2) {
return result;
}
int mask = 0;
const int MSB = 30;
for(int i = MSB; i >= 0; --i) {
mask |= (1 << i);
unordered_set<int> prefixes;
for(int k = 0; k < n; ++k) {
prefixes.insert(nums[k] & mask);
}
int curr = result | (1 << i);
for(auto elem: prefixes) {
if(prefixes.find((int)elem ^ curr) != prefixes.end()) {
result = curr;
break;
}
}
}
return result;
}
};