Leetcode--Recover Binary Search Tree

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Problem Description:

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

Recover the tree without changing its structure.

confused what "{1,#,2,3}" means? > read more on how binary tree is serialized on OJ.

   1
  /  2   3
    /
   4
         5

/**
 * 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 *pre,*p1,*p2;
    
    void helper(TreeNode *root)
    {
        if(root==NULL)
            return;
        helper(root->left);
        if(pre&&pre->val>root->val)//找到第一对逆序的两个数
        {
            if(p1==NULL)//先找到p1
            {
                p1=pre;
                p2=root;
            }
        
            else//如果找到第二对逆序的两个数则是p2
            {
                p2=root;
            }
        }
        pre=root;//先将pre初始化为root
        helper(root->right);
    }


    void recoverTree(TreeNode *root) {
        if(root==NULL)
            return;
        pre=p1=p2=NULL;
        helper(root);
        int temp;
        temp=p1->val;
        p1->val=p2->val;
        p2->val=temp;
        return;
    }
};

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Leetcode--Recover Binary Search Tree

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原文地址：http://blog.csdn.net/longhopefor/article/details/38444695