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Copy path_95.java
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52 lines (44 loc) · 1.31 KB
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package com.fishercoder.solutions;
import com.fishercoder.common.classes.TreeNode;
import java.util.ArrayList;
import java.util.List;
/**Given an integer n, generate all structurally unique BST's (binary search trees) that store values 1...n.
For example,
Given n = 3, your program should return all 5 unique BST's shown below.
1 3 3 2 1
\ / / / \ \
3 2 1 1 3 2
/ / \ \
2 1 2 3*/
public class _95 {
public List<TreeNode> generateTrees_pure_recursion(int n) {
List<TreeNode> result = new ArrayList<TreeNode>();
if (n == 0)
return result;
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;
}
if (start == end) {
result.add(new TreeNode(start));
return result;
}
for (int i = start; i <= end; i++) {
List<TreeNode> leftList = generateTrees(start, i - 1);
List<TreeNode> rightList = generateTrees(i + 1, end);
for (TreeNode left : leftList) {
for (TreeNode right : rightList) {
TreeNode root = new TreeNode(i);
root.left = left;
root.right = right;
result.add(root);
}
}
}
return result;
}
}