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从BST中移除一个节点是比较复杂的问题，需要分好几种情况讨论。
如这篇文章，就讨论了删除节点 1.有无左右子树 2.只有右子树 3.只有左子树 三种情况。
一种简单些的思维是只考虑删除节点是否有右子树（因为第一个比删除节点大的节点可能出现在右子树，不会出现在左子树）。
这里用Target表示删除节点，Parent表示删除节点的母节点。
1. 没有右子树
Parent.left / Parent.right = Target.left
2. 有右子树
1) 找到第一个比删除节点大的节点Node
2) 删除该节点Node
3) Target.val = Node.val 或 保留 Node 删除Target
/**
* Definition of TreeNode:
* public class TreeNode {
* public int val;
* public TreeNode left, right;
* public TreeNode(int val) {
* this.val = val;
* this.left = this.right = null;
* }
* }
*/
public class Solution {
/**
* @param root: The root of the binary search tree.
* @param value: Remove the node with given value.
* @return: The root of the binary search tree after removal.
*/
public TreeNode removeNode(TreeNode root, int value) {
// write your code here
TreeNode dummy = new TreeNode(0);
dummy.left = root;
TreeNode parent = findNodeParent(dummy, root, value);
TreeNode target;
if (parent.left != null && parent.left.val == value) {
target = parent.left;
} else if (parent.right != null && parent.right.val == value) {
target = parent.right;
} else {
return dummy.left;
}
deleteNode(parent, target);
return dummy.left;
}
private TreeNode findNodeParent(TreeNode parent, TreeNode node, int val) {
if (node == null || node.val == val) {
return parent;
}
if (node.val < val) {
return findNodeParent(node, node.right, val);
} else {
return findNodeParent(node, node.left, val);
}
}
private void deleteNode(TreeNode parent, TreeNode target) {
if (target.right == null) {
if (parent.right == target) {
parent.right = target.left;
} else {
parent.left = target.left;
}
} else {
// Find first element that is greater than target
TreeNode node1 = target.right;
TreeNode node2 = target;
while (node1.left != null) {
node2 = node1;
node1 = node1.left;
}
// Remove node1
if (node1 == node2.left) {
node2.left = node1.right;
} else {
node2.right = node1.right;
}
// Remove target
if (target == parent.right) {
parent.right = node1;
} else {
parent.left = node1;
}
node1.left = target.left;
node1.right = target.right;
}
}
}
Remove Node in Binary Search Tree 解答
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原文地址：http://www.cnblogs.com/ireneyanglan/p/5972522.html
