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LeetCode-95-Unique-Binary-Search-Trees-II.java
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LeetCode-95-Unique-Binary-Search-Trees-II.java
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/*
LeetCode: https://leetcode.com/problems/unique-binary-search-trees-ii/
LintCode: http://www.lintcode.com/problem/unique-binary-search-trees-ii/
JiuZhang: http://www.jiuzhang.com/solutions/unique-binary-search-trees-ii/
ProgramCreek: http://www.programcreek.com/2014/05/leetcode-unique-binary-search-trees-ii-java/
Analysis:
Root is from min to max
Left tree is min~i-1, we assume has L unique left trees; right is i+1~max, we assume has R unique right trees.
We generate all possible left & right tree, and put left tree and right tree to root.
*/
/**
* Definition for a binary tree node.
* public class TreeNode {
* int val;
* TreeNode left;
* TreeNode right;
* TreeNode(int x) { val = x; }
* }
*/
public class Solution {
public List<TreeNode> generateTrees(int n) {
if(n == 0) return new ArrayList<TreeNode>();
return generateTrees(1, n);
}
private List<TreeNode> generateTrees(int start, int end){
List<TreeNode> result = new ArrayList<TreeNode>();
if(start > end){
result.add(null);
return result;
}
for(int i = start; i <= end; i++){
List<TreeNode> left = generateTrees(start, i - 1);
List<TreeNode> right = generateTrees(i + 1, end);
for(TreeNode l : left){
for(TreeNode r : right){
TreeNode node = new TreeNode(i);
node.left = l;
node.right = r;
result.add(node);
}
}
}
return result;
}
}