Create Solution.java

This works.

Author: 361930

solution/1900-1999/1938.Maximum Genetic Difference Query/Solution.java

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+class TrieNode {
+  public TrieNode[] children = new TrieNode[2];
+  public int count = 0;
+}
+
+class Trie {
+  public void update(int num, int val) {
+    TrieNode node = root;
+    for (int i = HEIGHT; i >= 0; --i) {
+      final int bit = (num >> i) & 1;
+      if (node.children[bit] == null)
+        node.children[bit] = new TrieNode();
+      node = node.children[bit];
+      node.count += val;
+    }
+  }
+
+  public int query(int num) {
+    int ans = 0;
+    TrieNode node = root;
+    for (int i = HEIGHT; i >= 0; --i) {
+      final int bit = (num >> i) & 1;
+      final int targetBit = bit ^ 1;
+      if (node.children[targetBit] != null && node.children[targetBit].count > 0) {
+        ans += 1 << i;
+        node = node.children[targetBit];
+      } else {
+        node = node.children[targetBit ^ 1];
+      }
+    }
+    return ans;
+  }
+
+  private static final int HEIGHT = 17;
+  TrieNode root = new TrieNode();
+}
+
+class Solution {
+  public int[] maxGeneticDifference(int[] parents, int[][] queries) {
+    final int n = parents.length;
+    int[] ans = new int[queries.length];
+    int rootVal = -1;
+    List<Integer>[] tree = new List[n];
+
+    for (int i = 0; i < n; ++i)
+      tree[i] = new ArrayList<>();
+
+    // {node: (index, val)}
+    Map<Integer, List<Pair<Integer, Integer>>> nodeToQueries = new HashMap<>();
+    Trie trie = new Trie();
+
+    for (int i = 0; i < parents.length; ++i)
+      if (parents[i] == -1)
+        rootVal = i;
+      else
+        tree[parents[i]].add(i);
+
+    for (int i = 0; i < queries.length; ++i) {
+      final int node = queries[i][0];
+      final int val = queries[i][1];
+      nodeToQueries.putIfAbsent(node, new ArrayList<>());
+      nodeToQueries.get(node).add(new Pair<>(i, val));
+    }
+
+    dfs(rootVal, trie, tree, nodeToQueries, ans);
+    return ans;
+  }
+
+  private void dfs(int node, Trie trie, List<Integer>[] tree,
+                   Map<Integer, List<Pair<Integer, Integer>>> nodeToQueries, int[] ans) {
+    trie.update(node, 1);
+
+    if (nodeToQueries.containsKey(node))
+      for (Pair<Integer, Integer> query : nodeToQueries.get(node)) {
+        final int i = query.getKey();
+        final int val = query.getValue();
+        ans[i] = trie.query(val);
+      }
+
+    for (final int child : tree[node])
+      dfs(child, trie, tree, nodeToQueries, ans);
+
+    trie.update(node, -1);
+  }
+}