#include<stdio.h>
#include<stdlib.h>
#include<stdbool.h>
// Assumed int size
#define INT_SIZE 32
// A Trie Node
struct TrieNode
{
int value; // Only used in leaf nodes
struct TrieNode *arr[2];
};
// Utility function tp create a Trie node
struct TrieNode *newNode()
{
struct TrieNode *temp =malloc(sizeof(struct TrieNode));
temp->value = 0;
temp->arr[0] = temp->arr[1] = NULL;
return temp;
}
// Inserts pre_xor to trie with given root
void insert(struct TrieNode *root, int pre_xor)
{
struct TrieNode *temp = root;
// Start from the msb, insert all bits of
// pre_xor into Trie
for (int i=INT_SIZE-1; i>=0; i--)
{
// Find current bit in given prefix
bool val = pre_xor & (1<<i);
// Create a new node if needed
if (temp->arr[val] == NULL)
temp->arr[val] = newNode();
temp = temp->arr[val];
}
// Store value at leaf node
temp->value = pre_xor;
}
// Finds the maximum XOR ending with last number in
// prefix XOR 'pre_xor' and returns the XOR of this maximum
// with pre_xor which is maximum XOR ending with last element
// of pre_xor.
int query(struct TrieNode *root, int pre_xor)
{
struct TrieNode *temp = root;
for (int i=INT_SIZE-1; i>=0; i--)
{
// Find current bit in given prefix
bool val = pre_xor & (1<<i);
// Traverse Trie, first look for a
// prefix that has opposite bit
if (temp->arr[1-val]!=NULL)
temp = temp->arr[1-val];
// If there is no prefix with opposite
// bit, then look for same bit.
else if (temp->arr[val] != NULL)
temp = temp->arr[val];
}
return pre_xor^(temp->value);
}
int max(int result,int x)
{
return (result > x )?result:x;
}
// Returns maximum XOR value of a subarray in arr[0..n-1]
int maxSubarrayXOR(int arr[], int n)
{
// Create a Trie and insert 0 into it
struct TrieNode *root = newNode();
insert(root, 0);
// Initialize answer and xor of current prefix
int result = INT_SIZE;
int pre_xor =0;
// Traverse all input array element
for (int i=0; i<n; i++)
{
// update current prefix xor and insert it into Trie
pre_xor = pre_xor^arr[i];
insert(root, pre_xor);
// Query for current prefix xor in Trie and update
// result if required
int result = max(result, query(root, pre_xor));
}
return result;
}
// Driver program to test above functions
int main()
{
int arr[] = {8, 1, 2, 12};
int n = sizeof(arr)/sizeof(arr[0]); int result;
printf("Max subarray XOR is %d", result);
return 0;
}
Output:
Max subarray XOR is 21870
