114. Flatten Binary Tree to Link

题目链接

https://leetcode.com/problems/flatten-binary-tree-to-linked-list/

代码

class Solution {
public:
    void flatten(TreeNode* root) {
        TreeNode* cur = NULL;
        dfs(root, cur);
    }

    void dfs(TreeNode* parent, TreeNode*& cur) {
        if (parent == NULL) {
            return;
        }
        TreeNode* right = parent->right;
        TreeNode* left = parent->left;
        if (cur == NULL) {
            cur = parent;
            cur->right = NULL;
            cur->left = NULL;
        } else {
            cur->right = parent;
            cur->left = NULL;
            cur = parent;
        }

        dfs(left, cur);
        dfs(right, cur);
    }
};