Flatten Binary Tree to Linked List
/**
* Definition for binary tree
* struct TreeNode {
* int val;
* TreeNode *left;
* TreeNode *right;
* TreeNode(int x) : val(x), left(NULL), right(NULL) {}
* };
*/
class Solution {
public:
void flatten(TreeNode *r, TreeNode *&pre) {
if (!r) return;
TreeNode *left = r->left, *right = r->right;
if (pre == NULL) {
pre = r;
pre->left = pre->right = NULL;
} else {
pre->right = r;
r->left = NULL;
pre = r;
}
flatten(left, pre);
flatten(right, pre);
}
void flatten(TreeNode *root) {
TreeNode *pre = NULL;
flatten(root, pre);
if (pre)
pre->right = NULL;
}
};