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Preface
I learned JAVA for a day today. In the last hour of today, I will write a tree problem. I learned this topic from Dongge, and then record it now. I hope I will learn all the methods tomorrow.
Binary tree expands into linked list
Title description
Problem analysis
The idea is to first turn the left subtree into a linked list, then turn the right one into a linked list, and finally insert the right one to the end of the left subtree linked list.
Implementation code
class Solution {
public void flatten(TreeNode root) {
if(root == null){
return;
}
//将左子树拉成链表
flatten(root.left);
//将右子树拉成链表
flatten(root.right);
//定义一个指针用来指向左子树的头
TreeNode left = root.left;
//定义一个指针用来指向左子树的头
TreeNode right = root.right;
//清空根节点的左子树，因为我们要整成链表
root.left = null;
root.right = left;
TreeNode p =root;
//遍历到链表尾部
while(p.right!=null){
p = p.right;
}
//将右子树接到左子树上面
p.right = right;
}
}