0.code
/*
// Definition for a Node.
class Node {
public int val;
public Node left;
public Node right;
public Node() {}
public Node(int _val) {
val = _val;
}
public Node(int _val,Node _left,Node _right) {
val = _val;
left = _left;
right = _right;
}
};
*/
class Solution {
Node pre,head;
public Node treeToDoublyList(Node root) {
if(root==null){
return null;
}
head = root;
dfs(root);
head.left = pre;
pre.right = head;
return head;
}
public void dfs(Node root){
if(root==null){
return;
}
dfs(root.left);
if(pre==null){
head = root;
pre = head;
}else{
pre.right = root;
root.left = pre;
}
pre = root;
dfs(root.right);
}
}
