flatten-binary-tree-to-linked-list.cc

#include <algorithm>
#include <stack>

using namespace std;

// Definition for a binary tree node.
struct TreeNode {
    TreeNode() : value(0), left(nullptr), right(nullptr) {}
    TreeNode(int x) : value(x), left(nullptr), right(nullptr) {}
    TreeNode(int x, TreeNode *left, TreeNode *right) : value(x), left(left), right(right) {}

    int       value;
    TreeNode *left;
    TreeNode *right;
};

class Solution {
  public:
    void flatten(TreeNode *root) {
        if (root == nullptr) return;
        flatten(root->left);
        flatten(root->right);
        TreeNode *temp = root->right;
        root->right    = root->left;
        root->left     = nullptr;
        while (root->right != nullptr) root = root->right;
        root->right = temp;
    }
};

inline TreeNode *TN(int x, TreeNode *left = nullptr, TreeNode *right = nullptr) {
    return new TreeNode(x, left, right);
}

int main(int argc, char const *argv[]) {
    Solution  solution;
    TreeNode *root = TN(1, TN(2, TN(3), TN(4)), TN(5, nullptr, TN(6)));
    solution.flatten(root);
}