Recover Binary Search Tree

Two elements of a binary search tree (BST) are swapped by mistake.

Recover the tree without changing its structure.

 1 public class Solution {
 2     public void recoverTree(TreeNode root) {
 3         if(root==null) return ;
 4         ArrayList<TreeNode> t = new ArrayList<TreeNode> ();
 5         ArrayList<Integer> v = new ArrayList<Integer> ();
 6         get(root,t,v);
 7         Collections.sort(v);
 8         for(int i=0;i<v.size();i++){
 9             t.get(i).val = v.get(i);
10         }
11     }
12     public void get(TreeNode root,ArrayList<TreeNode> t,ArrayList<Integer> v){
13         if(root==null) return ;
14         get(root.left,t,v);
15         t.add(root);
16         v.add(root.val);
17         get(root.right,t,v);
18     }
19 }
View Code 
 1 public class Solution {
 2    public void recoverTree(TreeNode root) {
 3        TreeNode cur,parent = null,pre,f1=null,f2=null;
 4        boolean Found = false;
 5        cur = root;
 6        if(root==null) return ;
 7        while(cur!=null){
 8            if(cur.left==null){
 9                if(parent!=null && parent.val> cur.val){
10                    if(!Found){
11                        Found=true;
12                        f1 = parent;
13                    }
14                     f2 = cur;
15                }
16                parent = cur;
17                cur = cur.right;
18            }
19            else{
20                /* Find the inorder predecessor of current */
21                pre = cur.left;
22                while(pre.right!=null && pre.right!=cur){
23                    pre = pre.right;
24                }
25                /* Make current as right child of its inorder predecessor */
26                if(pre.right==null){
27                    pre.right = cur;
28                    cur = cur.left;
29                }
30                /* Revert the changes made in if part to restore the original
31                    tree i.e., fix the right child of predecssor */  
32                else {
33                    pre.right =null;
34                    if(parent!=null && parent.val> cur.val){
35                    if(!Found){
36                        Found=true;
37                        f1 = parent;//should not use else
38                    }
39                    f2 = cur;
40                }
41                parent = cur;
42                cur = cur.right;
43                }
44            }
45        }
46        if(f1!=null && f2!=null){
47            int temp = f1.val;
48            f1.val = f2.val;
49            f2.val = temp;
50        }
51    }
52 }
View Code

 

posted @ 2014-02-17 01:40  krunning  阅读(231)  评论(0)  编辑  收藏  举报