我有以下代码来查找最低的公共(public)祖先(具有 a 和 b 作为后代的最低节点):
public static Node LCA(Node root, Node a, Node b)
{
if (root == null)
return null;
if (root.IData == a.IData || root.IData == b.IData)
return root;
if (root.RightChild != null && (root.RightChild.IData == a.IData || root.RightChild.IData == b.IData))
return root;
if (root.LeftChild != null && (root.LeftChild.IData == a.IData || root.LeftChild.IData == b.IData))
return root;
if (root.IData > a.IData && root.IData > b.IData)
return LCA(root.LeftChild, a, b);
else if (root.IData < a.IData && root.IData < b.IData)
return LCA(root.RightChild, a, b);
else
return root;
}
二叉搜索树是 20
/ \
8 22
/ \
4 12
/ \
10 14
问题 它在以下情况下失败:
有什么想法吗?
节点在哪里
class Node
{
public int IData {get; set;}
public Node RightChild {get; set;}
public Node LeftChild {get; set;}
}
最佳答案
如果 IData
的 root
与 a
和 b
都不同,但 root
的一个子代与两者之一具有相同的 IData
,则返回 root
,但根据您的定义,如果两个节点都在同一个子树中。由于您还想检查两个节点是否实际上都在树中,因此必须在任何返回之前执行该检查。
public static Node LCA(Node root, Node a, Node b)
{
if (root == null) return null;
// what if a == null or b == null ?
Node small, large, current = root;
if (a.IData < b.IData)
{
small = a;
large = b;
}
else
{
small = b;
large = a;
}
if (large.IData < current.IData)
{
do
{
current = current.LeftChild;
}while(current != null && large.IData < current.IData);
if (current == null) return null;
if (current.IData < small.IData) return LCA(current,small,large);
// if we get here, current has the same IData as one of the two, the two are
// in different subtrees, or not both are in the tree
if (contains(current,small) && contains(current,large)) return current;
// at least one isn't in the tree, return null
return null;
}
else if (current.IData < small.IData)
{
// the symmetric case, too lazy to type it out
}
else // Not both in the same subtree
{
if (contains(current,small) && contains(current,large)) return current;
}
return null; // at least one not in tree
}
public static bool contains(Node root, Node target)
{
if (root == null) return false;
if (root.IData == target.IData) return true;
if (root.IData < target.IData) return contains(root.RightChild,target);
return contains(root.LeftChild,target);
}
关于c# - 在二叉搜索树中找到最低的共同祖先,我们在Stack Overflow上找到一个类似的问题:https://stackoverflow.com/questions/8441331/