二叉树的下一个节点

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode *father;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL), father(NULL) {}
 * };
 */
class Solution {
public:
    TreeNode* inorderSuccessor(TreeNode* p) {
        if(p->right)//如果有右儿子，找到右子树最左侧的点
        {
            p=p->right;
            while(p->left)   p=p->left;
            return p;
        }
        //否则向右上找父节点
        while(p->father&&p!=p->father->left)
            p=p->father;
        return p->father;
    }
};