|
| 1 | +/* |
| 2 | + Author: Andy, nkuwjg@gmail.com |
| 3 | + Date: Jan 28, 2015 |
| 4 | + Problem: Flatten Binary Tree to Linked List |
| 5 | + Difficulty: Medium |
| 6 | + Source: https://oj.leetcode.com/problems/flatten-binary-tree-to-linked-list/ |
| 7 | + Notes: |
| 8 | + Given a binary tree, flatten it to a linked list in-place. |
| 9 | + For example, |
| 10 | + Given |
| 11 | + 1 |
| 12 | + / \ |
| 13 | + 2 5 |
| 14 | + / \ \ |
| 15 | + 3 4 6 |
| 16 | + The flattened tree should look like: |
| 17 | + 1 |
| 18 | + \ |
| 19 | + 2 |
| 20 | + \ |
| 21 | + 3 |
| 22 | + \ |
| 23 | + 4 |
| 24 | + \ |
| 25 | + 5 |
| 26 | + \ |
| 27 | + 6 |
| 28 | + Hints: |
| 29 | + If you notice carefully in the flattened tree, each node's right child points to the next node |
| 30 | + of a pre-order traversal. |
| 31 | +
|
| 32 | + Solution: Recursion. Return the last element of the flattened sub-tree. |
| 33 | + */ |
| 34 | + |
| 35 | +/** |
| 36 | + * Definition for binary tree |
| 37 | + * public class TreeNode { |
| 38 | + * int val; |
| 39 | + * TreeNode left; |
| 40 | + * TreeNode right; |
| 41 | + * TreeNode(int x) { val = x; } |
| 42 | + * } |
| 43 | + */ |
| 44 | +publicclassSolution { |
| 45 | +publicvoidflatten(TreeNoderoot) { |
| 46 | +flatten_3(root); |
| 47 | + } |
| 48 | +publicvoidflatten_1(TreeNoderoot) { |
| 49 | +if (root ==null)return; |
| 50 | +flatten_1(root.left); |
| 51 | +flatten_1(root.right); |
| 52 | +if (root.left ==null)return; |
| 53 | +TreeNodenode =root.left; |
| 54 | +while (node.right !=null)node =node.right; |
| 55 | +node.right =root.right; |
| 56 | +root.right =root.left; |
| 57 | +root.left =null; |
| 58 | + } |
| 59 | +publicvoidflatten_2(TreeNoderoot) { |
| 60 | +if (root ==null)return; |
| 61 | +Stack<TreeNode>stk =newStack<TreeNode>(); |
| 62 | +stk.push(root); |
| 63 | +while (stk.empty() ==false) { |
| 64 | +TreeNodecur =stk.pop(); |
| 65 | +if (cur.right !=null)stk.push(cur.right); |
| 66 | +if (cur.left !=null)stk.push(cur.left); |
| 67 | +cur.left =null; |
| 68 | +cur.right =stk.empty() ==true ?null :stk.peek(); |
| 69 | + } |
| 70 | + } |
| 71 | +publicTreeNodeflattenRe3(TreeNoderoot,TreeNodetail) { |
| 72 | +if (root ==null)returntail; |
| 73 | +root.right =flattenRe3(root.left,flattenRe3(root.right,tail)); |
| 74 | +root.left =null; |
| 75 | +returnroot; |
| 76 | + } |
| 77 | +publicvoidflatten_3(TreeNoderoot) { |
| 78 | +if (root ==null)return; |
| 79 | +flattenRe3(root,null); |
| 80 | + } |
| 81 | +} |
| 82 | + |
