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-rw-r--r--max_xor_two_num_arr.c87
1 files changed, 87 insertions, 0 deletions
diff --git a/max_xor_two_num_arr.c b/max_xor_two_num_arr.c
new file mode 100644
index 0000000..70765fd
--- /dev/null
+++ b/max_xor_two_num_arr.c
@@ -0,0 +1,87 @@
+// 421. Maximum XOR of Two Numbers in an Array
+#include "leetcode.h"
+
+/*
+ * given an integer array 'nums', return the maximum result of 'nums[i] ^
+ * nums[j]' where '0 <= i <= j < n'
+ */
+
+struct tree {
+ struct tree *left;
+ struct tree *right;
+};
+
+static int ans;
+struct tree *root;
+
+struct tree *new_node(void) {
+ struct tree *obj = (struct tree *)malloc(sizeof(struct tree));
+ obj->left = NULL;
+ obj->right = NULL;
+ return obj;
+}
+
+void trie_create(struct tree *r, int n, int width) {
+ if (width <= 0 || !r)
+ return;
+ if (n & (1 << (width - 1))) {
+ if (!r->right)
+ r->right = new_node();
+ trie_create(r->right, n, width - 1);
+ } else {
+ if (!r->left)
+ r->left = new_node();
+ trie_create(r->left, n, width - 1);
+ }
+ return;
+}
+
+void max_xor(struct tree *high, struct tree *low, int xor, int bit_pos) {
+ bool skip = false;
+ if (!low) {
+ ans = ans < xor ? xor : ans;
+ return;
+ }
+ if (high->right && low->left) {
+ xor |= 1 << (bit_pos - 1);
+ max_xor(high->right, low->left, xor, bit_pos - 1);
+ xor &= ~(1 << (bit_pos - 1));
+ skip = true;
+ }
+ if (high->left && low->right) {
+ xor |= 1 << (bit_pos - 1);
+ max_xor(high->left, low->right, xor, bit_pos - 1);
+ xor &= ~(1 << (bit_pos - 1));
+ skip = true;
+ }
+ if (!skip) {
+ max_xor(high->left, low->left, xor, bit_pos - 1);
+ max_xor(high->right, high->right, xor, bit_pos - 1);
+ }
+}
+
+int findMaximumXOR(int *nums, int numsSize) {
+ struct tree *node = root;
+ int num, max = -1, bit_pos = 0, xor = 0;
+ for (int i = 0; i < numsSize; i++)
+ max = max < nums[i] ? nums[i] : max;
+ while (max) {
+ bit_pos++;
+ max >>= 1;
+ }
+ root = new_node();
+ for (int i = 0; i < numsSize; i++)
+ trie_create(root, nums[i], bit_pos);
+ struct tree *high, *low;
+ high = low = root;
+ ans = 0;
+ max_xor(root, root, 0, bit_pos);
+ return ans;
+}
+
+int main() {
+ int n1[] = {3, 10, 5, 25, 2, 8},
+ n2[] = {14, 70, 53, 83, 49, 91, 36, 80, 92, 51, 66, 70};
+ printf("%d\n", findMaximumXOR(n1, ARRAY_SIZE(n1))); // expect: 28
+ printf("%d\n", findMaximumXOR(n2, ARRAY_SIZE(n2))); // expect: 127
+}