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783. Minimum Distance Between BST Nodes 👍

  • Time: $O(n)$
  • Space: $O(\log n) \to O(n)$
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class Solution {
 public:
  int minDiffInBST(TreeNode* root) {
    int ans = INT_MAX;

    inorder(root, ans);

    return ans;
  }

 private:
  int pred = -1;

  void inorder(TreeNode* root, int& ans) {
    if (!root)
      return;

    inorder(root->left, ans);
    if (pred >= 0)
      ans = min(ans, root->val - pred);
    pred = root->val;
    inorder(root->right, ans);
  }
};
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class Solution {
  public int minDiffInBST(TreeNode root) {
    inorder(root);
    return ans;
  }

  private int ans = Integer.MAX_VALUE;
  private Integer pred = null;

  private void inorder(TreeNode root) {
    if (root == null)
      return;

    inorder(root.left);
    if (pred != null)
      ans = Math.min(ans, root.val - pred);
    pred = root.val;
    inorder(root.right);
  }
}
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