421

Author: lzl124631x

leetcode/421. Maximum XOR of Two Numbers in an Array/README.md

@@ -61,29 +61,33 @@ struct TrieNode {
     TrieNode *next[2] = {};
 };
 class Solution {
-    void addNode(TrieNode *node, int n) {
+    void add(TrieNode *node, int n) {
         for (int i = 31; i >= 0; --i) {
-            int bit = (n >> i) & 1;
-            if (!node->next[bit]) node->next[bit] = new TrieNode();
-            node = node->next[bit];
+            int b = n >> i & 1;
+            if (node->next[b] == NULL) node->next[b] = new TrieNode();
+            node = node->next[b];
         }
     }
+    int maxXor(TrieNode *node, int n) {
+        int ans = 0;
+        for (int i = 31; i >= 0; --i) {
+            int b = n >> i & 1;
+            if (node->next[1 - b]) { // if we can go the opposite direction, do it.
+                node = node->next[1 - b];
+                ans |= 1 << i;
+            } else {
+                node = node->next[b];
+            }
+        }
+        return ans;
+    }
 public:
     int findMaximumXOR(vector<int>& A) {
         TrieNode root;
-        for (int n : A) addNode(&root, n);
         int ans = 0;
         for (int n : A) {
-            auto node = &root;
-            int val = 0;
-            for (int i = 31; i >= 0; --i) {
-                int bit = (n >> i) & 1;
-                if (node->next[1 ^ bit]) {
-                    val |= 1 << i;
-                    node = node->next[1 ^ bit];
-                } else node = node->next[bit];
-            }
-            ans = max(ans, val);
+            add(&root, n);
+            ans = max(ans, maxXor(&root, n));
         }
         return ans;
     }