二叉排序树删除节点

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#include<iostream>using namespace std;class TreeNode {public:    int val;    TreeNode *left, *right;    TreeNode(int val) {        this->val = val;        this->left = this->right = NULL;    }};class Solution {public:    TreeNode* removeNode(TreeNode* root, int val) {        // if root is null, just return        if (!root)           return root;         // Find node whose val equal to "val"        TreeNode* parent = NULL;        TreeNode* curr = root;        while (curr) {            if (curr->val == val)                 break;            parent = curr;            if (curr->val > val)                curr = curr->left;            else                curr = curr->right;        }        // If there is no node's value equals to val        if (!curr)            return root;                // Situation 1, leafe node        if (!curr->left && !curr->right) {            if (!parent) {                root = NULL;            } else {                if (parent->left == curr)                     parent->left = NULL;                else                     parent->right = NULL;            }            delete curr;        } else if (curr->left && !curr->right) {            // Situation 2, no right child            if (!parent) {                root = curr->left;            } else {                if (parent->left == curr)                     parent->left = curr->left;                else                     parent->right = curr->left;            }            delete curr;        } else if (!curr->left && curr->right) {            // Situation 3, no left child            if (!parent) {                root = curr->right;            } else {                if (parent->left == curr)                     parent->left = curr->right;                else                   parent->right = curr->right;             }             delete curr;        } else {            // Situation 4, both childs are existing            TreeNode* left_max = curr->left;            parent = curr;             while (left_max->right) {                parent = left_max;                left_max = left_max->right;             }                        // Swap with curr node            curr->val = curr->val ^ left_max->val;            left_max->val = curr->val ^ left_max->val;            curr->val = curr->val ^ left_max->val;                        // Delete left_max            if (parent->left == left_max)                parent->left = NULL;            else if (parent->right == left_max)                parent->right = NULL;            delete left_max;        }               return root;    }};void pLevel(TreeNode* node) {    if (!node)        return;    cout << node->val << endl;    pLevel(node->left);    pLevel(node->right);}int main() {    TreeNode* node5 = new TreeNode(5);    TreeNode* node3 = new TreeNode(3);    TreeNode* node6 = new TreeNode(6);    TreeNode* node2 = new TreeNode(2);    TreeNode* node4 = new TreeNode(4);    node5->left = node3;    node5->right = node6;    node3->left = node2;    node3->right = node4;    Solution s;    TreeNode* ret = s.removeNode(node5, 3);    pLevel(ret);    return 0;}
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