99. Recover Binary Search Tree
Description
Two elements of a binary search tree (BST) are swapped by mistake.
Recover the tree without changing its structure.
Constraints
Approach
Links
Examples
Input: [1, 3, null, null, 2]

Output: [3, 1, null, null, 2]

Solutions
// Definition for a binary tree node.
public class TreeNode {
int val;
TreeNode left;
TreeNode right;
TreeNode() {}
TreeNode(int val) { this.val = val; }
TreeNode(int val, TreeNode left, TreeNode right) {
this.val = val;
this.left = left;
this.right = right;
}
}
Follow up
A solution using O(n) space is pretty straight forward.
Could you devise a constant space solution?
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