Poison

114. Flatten Binary Tree to Linked List

发表于
Iterate
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class Solution {
    public void flatten(TreeNode root) {
        TreeNode curr = root;
        while (curr != null) {
            if (curr.left != null) {
                TreeNode leftRoot = curr.left;
                curr.left = null;
                TreeNode rightRoot = curr.right;
                curr.right = leftRoot;
                TreeNode tmp = leftRoot;
                while (tmp.right != null) {
                    tmp = tmp.right;
                }

                tmp.right = rightRoot;
            }

            curr = curr.right;
        }
    }
}
Recursion
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class Solution {
    public void flatten(TreeNode root) {
        // root, left, right

        if (root == null) {
            return;
        }

        if (root.left == null) {
            flatten(root.right);
        } else {
            TreeNode right = root.right;
            flatten(root.left);
            TreeNode tail = root.left;
            while (tail.right != null) {
                tail = tail.right;
            }
            tail.right = right;
            root.right = root.left;
            root.left = null;

            flatten(root.right); // 不要忘记最左子树展开后继续对剩余的右子树进行展开
        }
    }
}
Recursion
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class Solution {
    public void flatten(TreeNode root) {
        if (root == null) {
            return;
        }

        flatten(root.left);
        flatten(root.right);

        TreeNode leftRoot = root.left;
        TreeNode rightRoot = root.right;

        root.left = null;
        root.right = leftRoot;

        TreeNode curr = root;
        while (curr.right != null) {
            curr = curr.right;
        }
        curr.right = rightRoot;
    }
}
Reference

114. Flatten Binary Tree to Linked List