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程式語言 - LeetCode - C++ - 99. Recover Binary Search Tree

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題目：


解答：

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
 *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
 *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
 * };
 */
class Solution {
public:
    void recoverTree(TreeNode* root) {
        TreeNode *p = nullptr;
        TreeNode *f = nullptr;
        TreeNode *s = nullptr;

        auto dfs = [&](this auto&& dfs, TreeNode* n, TreeNode*& pre, TreeNode*& first, TreeNode*& second) -> void {
            if (!n) {
                return; 
            }

            dfs(n->left, pre, first, second);

            if (pre && pre->val > n->val) {
                if (!first) {
                    first = pre;
                }
                second = n;
            }
            pre = n;

            dfs(n->right, pre, first, second);
        };

        dfs(root, p, f, s);
        swap(f->val, s->val);
    }
};