1+ import java .util .ArrayList ;
2+ import java .util .List ;
3+
4+ class TreeNode {
5+ int val ;
6+ TreeNode left ;
7+ TreeNode right ;
8+ TreeNode (int x ) {
9+ val = x ;
10+ }
11+ }
12+
13+ // DP
14+ class Solution {
15+ public List <TreeNode > generateTrees (int n ) {
16+ List <TreeNode >[] res = new List [n +1 ];
17+ res [0 ] = new ArrayList <TreeNode >();
18+ if (n == 0 ){
19+ return res [0 ];
20+ }
21+ res [0 ].add (null );
22+ res [1 ] = new ArrayList <TreeNode >();
23+ res [1 ].add (new TreeNode (1 ));
24+ for (int i =2 ; i <=n ; i ++){
25+ res [i ] = new ArrayList <TreeNode >();
26+ for (int j =1 ; j <=i ; j ++){
27+ for (TreeNode nodeL : res [j - 1 ]){
28+ for (TreeNode nodeR : res [i - j ]){
29+ TreeNode node = new TreeNode (j );
30+ node .left = nodeL ;
31+ node .right = cloneTrees (nodeR , j );
32+ res [i ].add (node );
33+ }
34+ }
35+ }
36+ }
37+ return res [n ];
38+ }
39+
40+ public TreeNode cloneTrees (TreeNode node , int offset ){
41+ if (node == null ){
42+ return null ;
43+ }
44+ TreeNode newNode = new TreeNode (node .val + offset );
45+ newNode .left = cloneTrees (node .left , offset );
46+ newNode .right = cloneTrees (node .right , offset );
47+ return newNode ;
48+ }
49+ }
50+
51+ // Recursive
52+ class Solution {
53+ public List <TreeNode > generateTrees (int n ) {
54+ return (n == 0 )?new ArrayList <TreeNode >(): geneTrees (1 , n );
55+ }
56+
57+ public TreeNode formatNode (int val , TreeNode left , TreeNode right ){
58+ TreeNode newNode = new TreeNode (val );
59+ newNode .left = left ;
60+ newNode .right = right ;
61+ return newNode ;
62+ }
63+
64+ public List <TreeNode > geneTrees (int lo , int hi ){
65+ List <TreeNode > res = new ArrayList <TreeNode >();
66+ for (int i =lo ; i <=hi ; i ++){
67+ for (TreeNode nodeL : geneTrees (lo , i - 1 )){
68+ for (TreeNode nodeR : geneTrees (i + 1 , hi )){
69+ res .add (formatNode (i , nodeL , nodeR ));
70+ }
71+ }
72+ }
73+ if (res .isEmpty ()){
74+ res .add (null );
75+ }
76+ return res ;
77+ }
78+ }
0 commit comments