[LeetCode] Recover Binary Search Tree

最新推荐文章于 2018-03-28 11:34:00 发布

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本文介绍了一种解决二叉搜索树中两个节点被错误交换的问题的方法。通过中序遍历找到被交换的节点，并在常数空间复杂度内恢复树的正确结构，确保了树的性质不变。

Recover Binary Search Tree:

Two elements of a binary search tree (BST) are swapped by mistake.

Recover the tree without changing its structure.

Note:
A solution using O(n) space is pretty straight forward. Could you devise a constant space solution?

/**
 * Definition for binary tree
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    TreeNode* w1,*w2;
    void recoverTree(TreeNode *root) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        
		w1=NULL;
		w2=NULL;
		TreeNode* pre=NULL;
		inorder(root,pre);

		assert(w1&&w2);
		swap(w1->val,w2->val);
    }
	void inorder(TreeNode* root,TreeNode*& pre)
	{
		if (!root )
			return ;
		inorder(root->left,pre);
		if (pre&& pre->val>=root->val)
		{
			if (w1==NULL)
			{
				w1=pre;
				w2=root;
			}
			else
			{
				w2=root;
			}
		}
		pre=root;
		inorder(root->right,pre);
	}
};