Recover BST
问题描述
Two elements of a binary search tree (BST) are swapped by mistake.
Recover the tree without changing its structure.
解决思路
递归思路。
中序遍历的过程中,第一个违反顺序的节点一定是错误节点的其中一个;第二个违反顺序的节点的下一个节点是另外一个错误节点。
程序
public class RecoverBST { private TreeNode pre = null; private TreeNode n1 = null; private TreeNode n2 = null; public void recoverBST(TreeNode root) { if (root == null) { return; } inorderTraversal(root); if (n1 != null && n2 != null) { int tmp = n1.val; n1.val = n2.val; n2.val = tmp; } } private void inorderTraversal(TreeNode root) { if (root==null) { return; } inorderTraversal(root.left); if (pre != null && pre.val > root.val) { n2 = root; // second error node's next if (n1 == null) { n1 = pre; // first error node } } pre = root; inorderTraversal(root.right); } }