1.题目
2.自己初解的思路及问题
略，直接看力扣题解
3.题解方法一：前序遍历（递归+迭代）
递归：
class Solution {
public void flatten(TreeNode root) {
List<TreeNode> list = new ArrayList<TreeNode>();
preorderTraversal(root, list);
int size = list.size();
for (int i = 1; i < size; i++) {
TreeNode prev = list.get(i - 1), curr = list.get(i);
prev.left = null;
prev.right = curr;
}
}
public void preorderTraversal(TreeNode root, List<TreeNode> list) {
if (root != null) {
list.add(root);
preorderTraversal(root.left, list);
preorderTraversal(root.right, list);
}
}
}
以下代码通过迭代实现前序遍历。
class Solution {
public void flatten(TreeNode root) {
List<TreeNode> list = new ArrayList<TreeNode>();
Deque<TreeNode> stack = new LinkedList<TreeNode>();
TreeNode node = root;
while (node != null || !stack.isEmpty()) {
while (node != null) {
list.add(node);
stack.push(node);
node = node.left;
}
node = stack.pop();
node = node.right;
}
int size = list.size();
for (int i = 1; i < size; i++) {
TreeNode prev = list.get(i - 1), curr = list.get(i);
prev.left = null;
prev.right = curr;
}
}
}
