【LeetCode】Recover Binary Search Tree

中序遍历的话BST应该递增，那么在中序遍历过程中检查是否有节点违反这一规则即可。

/**
 * Definition for binary tree
 * struct TreeNode {
 * int val;
 * TreeNode *left;
 * TreeNode *right;
 * TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    void errNodes(TreeNode *node, TreeNode *&prev, TreeNode **nodes) {
        if(NULL==node) return;
        errNodes(node->left, prev, nodes);
        if(prev&&prev->val>node->val)
        {
            nodes[1]=node;
            if(!nodes[0]) nodes[0]=prev;
        }
        prev=node;
        errNodes(node->right,prev,nodes);
    }
    void recoverTree(TreeNode *root) {
        if(NULL==root) return;
        TreeNode *nodes[2]={0};
        TreeNode *prev=NULL;
        errNodes(root,prev,nodes);
        if(nodes[0]&&nodes[1])
            swap(nodes[0]->val,nodes[1]->val);
    }
};