leetcode-114-Flatten-Binary-Tree-to-Linked-List

描述


Given a binary tree, flatten it to a linked list in-place.

For example, given the following tree:

1
2
3
4
5
1
/ \
2 5
/ \ \
3 4 6

The flattened tree should look like:

1
2
3
4
5
6
7
8
9
10
11
1
\
2
\
3
\
4
\
5
\
6

分析


利用栈来解决这个问题,当遇到右子树时先入栈,如果左子树不为空,将其作为右子树,如果左子树为空,出栈,将其作为右子树,不断迭代右子树,直到栈为空。

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 void flatten(TreeNode root) {
Stack<TreeNode> stack = new Stack<TreeNode>();
TreeNode p = root;
while(p != null || !stack.empty()) {
if (p.right != null) {
stack.push(p.right);
}
if (p.left != null) {
p.right = p.left;
p.left = null;
} else if (!stack.empty()) {
TreeNode tmp = stack.pop();
p.right = tmp;
}
p = p.right;
}
}
}

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题目来源