[leetcode] Flatten Binary Tree to Linked List

Again, the recursion principle, pretending the recursive call is a completed API from outside.
这样问题就归类成 左边flatten好的 和右边fallten好的tree 怎么结合了。。自然就出答案了

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public class Solution { public void flatten(TreeNode root) { flattening(root); return; } private TreeNode flattening(TreeNode root){ if (root == null) return null; TreeNode leftTail = flattening(root.left); TreeNode rightTail = flattening(root.right); if (root.left != null){ TreeNode temp = root.right; root.right = root.left; root.left = null; leftTail.right = temp; } if (rightTail != null){ return rightTail; } if (leftTail != null){ return leftTail; } return root; } }