lc99-Recover Binary Search Tree

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/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    void recoverTree(TreeNode* root) {
        TreeNode* cur = root;
        TreeNode* prev = nullptr;
        int prev_val = INT_MIN;
        TreeNode* prev_node = nullptr;
        int swapped_val = INT_MAX;
        TreeNode* swapped_node = nullptr;
        bool sf = false;
        while(cur) {
            if (cur -> left == nullptr) {
                if (!sf && swapped_val != INT_MAX && cur -> val > swapped_val) {
                    swapped_node -> val = prev_val;
                    prev_node -> val = swapped_val;
                    sf = true;
                }
                if (!sf && swapped_val == INT_MAX && cur -> val < prev_val) {
                    swapped_val = prev_val;
                    swapped_node = prev_node;
                    // cout << "swapped: " << prev_val<<" "<<swapped_val;
                }
                prev_node = cur;
                prev_val = cur -> val;
                cur = cur -> right;
            }
            else {
                // find the qianqu jiedian
                prev = cur -> left;
                while (prev -> right != nullptr && prev -> right != cur) {
                    prev = prev -> right;
                }
                if (prev -> right == nullptr) {
                    prev -> right = cur;
                    cur = cur -> left;
                }
                
                if (prev -> right == cur) {
                    prev -> right = nullptr;
                    if (!sf && swapped_val != INT_MAX && cur -> val > swapped_val) {
                        swapped_node -> val = prev_val;
                        prev_node -> val = swapped_val;
                        sf = true;
                    }
                    if (!sf && swapped_val == INT_MAX && cur -> val < prev_val) {
                        swapped_val = prev_val;
                        swapped_node = prev_node;
                    }
                    prev_node = cur;
                    prev_val = cur -> val;
                    cur = cur -> right;
                }
            }
        }
        if (!sf) {
            swapped_node -> val = prev_val;
            prev_node -> val = swapped_val;
            cout << "swapped: "<<prev_val<<" "<<swapped_val;
        }
    }
};