leetcode-897-Increasing-Order-Search-Tree

描述


Given a tree, rearrange the tree in in-order so that the leftmost node in the tree is now the root of the tree, and every node has no left child and only 1 right child.

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Example 1:
Input: [5,3,6,2,4,null,8,1,null,null,null,7,9]

5
/ \
3 6
/ \ \
2 4 8
/ / \
1 7 9

Output: [1,null,2,null,3,null,4,null,5,null,6,null,7,null,8,null,9]

1
\
2
\
3
\
4
\
5
\
6
\
7
\
8
\
9

Note:

  1. The number of nodes in the given tree will be between 1 and 100.
  2. Each node will have a unique integer value from 0 to 1000.

分析


中序遍历一颗二叉树。

解决方案1(Java)


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/**
* Definition for a binary tree node.
* public class TreeNode {
* int val;
* TreeNode left;
* TreeNode right;
* TreeNode(int x) { val = x; }
* }
*/
class Solution {
public TreeNode increasingBST(TreeNode root) {
List<Integer> vals = new ArrayList();
inOrder(root, vals);
TreeNode result = new TreeNode(0);
TreeNode current = result;
for (int v: vals) {
TreeNode newNode = new TreeNode(v);
current.right = newNode;
current = newNode;
}
return result.right;
}

private void inOrder(TreeNode node, List<Integer> vals) {
if (node == null) {
return;
}
inOrder(node.left, vals);
vals.add(node.val);
inOrder(node.right, vals);
}
}

题目来源