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Author: whd

421 Maximum XOR of Two Numbers in an Array .cpp

@@ -0,0 +1,42 @@
+class Solution {
+public:
+    int findMaximumXOR(vector<int>& nums) {
+        struct Node {
+            shared_ptr<Node> c[2];
+        };
+        using ptr = shared_ptr<Node>; 
+        ptr root(new Node());
+        auto insert = [&] (int num) {
+            ptr now = root;
+            for (int k = 30; k >= 0; k--) {
+                auto c = num >> k & 1;
+                if (!now->c[c]) {
+                    now->c[c] = ptr(new Node());
+                }
+                now = now->c[c];
+            }  
+        };
+        auto find = [&] (int num) {
+            ptr now = root;
+            int ans = 0;
+            for (int k = 30; k >= 0; k--) {
+                auto c = !(num >> k & 1);
+                if (now->c[c]) {
+                    ans += 1 << k;
+                } else {
+                    c = !c;
+                }
+                now = now->c[c];
+            }
+            return ans;
+        };
+        int ans = 0;
+        for (int i = 0; i < nums.size(); i++) {
+            if (i) {
+                ans = max(ans, find(nums[i]));
+            }
+            insert(nums[i]);
+        }
+        return ans;
+    }
+};