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import java.lang.*;
import java.util.*;
import node.*;
class BuildTree {
// My old solution
/*
public static TreeNode buildTree(int[] preorder, int[] inorder) {
TreeNode root = new TreeNode(preorder[0]);
Stack<TreeNode> stack = new Stack<TreeNode>();
stack.push(root);
int parentIndex = 1;
boolean left = true;
for (int i = 1; i < preorder.length; i++) {
TreeNode node = new TreeNode(preorder[i]);
for (int j = 0; j < inorder.length; j++) {
if (node.val == inorder[j]) {
if (j < parentIndex) {
left = true;
stack.peek().left = node;
System.out.println("Left: " + node.val);
} else if (left) {
left = false;
stack.pop();
stack.peek().right = node;
System.out.println("Right: " + node.val);
} else {
stack.peek().right = node;
System.out.println(stack.peek().val);
System.out.println("Right: " + node.val);
}
parentIndex = j;
break;
}
}
stack.push(node);
}
return root;
}
*/
private static int preIndex = 0;
public static int findInorder(int value, int[] inorder) {
for (int i = 0; i < inorder.length; i++) {
if (inorder[i] == value)
return i;
}
return -1;
}
public static TreeNode
buildTree(int[] preorder, int[] inorder, int start, int end) {
if (start > end)
return null;
int value = preorder[preIndex++];
TreeNode node = new TreeNode(value);
if (start == end)
return node;
int mid = findInorder(value, inorder);
node.left = buildTree(preorder, inorder, start, mid - 1);
node.right = buildTree(preorder, inorder, mid + 1, end);
return node;
}
public static void main(String[] args) {
TreeNode leftLeaf = new TreeNode(9);
TreeNode middleLeaf = new TreeNode(15);
TreeNode rightLeaf = new TreeNode(7);
TreeNode rightParent = new TreeNode(20, middleLeaf, rightLeaf);
TreeNode root = new TreeNode(3, leftLeaf, rightParent);
int[] preorder = {3, 9, 20, 15, 7};
int[] inorder = {9, 3, 15, 20, 7};
int n = preorder.length - 1;
System.out.println(buildTree(preorder, inorder, 0, n).right.right.val);
}
}
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