C++ 代码

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     struct TreeNode *left;
 *     struct TreeNode *right;
 *     struct TreeNode *father;
 * };
 */
struct TreeNode* inorderSuccessor(struct TreeNode* p) {
    if(p->right)    //有右孩子
    {   
        p = p->right;
        while(p->left)  p = p->left;    //右子树的最左儿子
        return p;
    } 
    else  if(p->father)   //没有右孩子，则回溯父节点
    {
        if(p == p->father->right)   return p->right;     //右子树适用，返回null
        if(p->father->right) return p->father;   //左子树适用,返回父节点
    }
}