[Leetcode] 105. Construct Binary Tree from Preorder and Inorder Traversal

/**
* Definition for binary tree
* public class TreeNode {
*     int val;
*     TreeNode left;
*     TreeNode right;
*     TreeNode(int x) { val = x; }
* }
*/
public class Solution {
public TreeNode buildTree(int[] preorder, int[] inorder) {
if(preorder == null || inorder == null || preorder.length == 0
|| inorder.length == 0 || preorder.length != inorder.length) return null;
return build(preorder, 0, preorder.length - 1, inorder, 0, inorder.length - 1);
}
private TreeNode build(int[] preorder, int prestart, int preend, int[] inorder, int instart, int inend){
if(prestart > preend) return null;
TreeNode root = new TreeNode(preorder[prestart]);
int position = findPosition(inorder, instart, inend, preorder[prestart]);
root.left = build(preorder, prestart + 1, prestart + position - instart, inorder, instart, position - 1);
root.right = build(preorder, prestart + position - instart + 1, preend, inorder, position + 1, inend);
return root;
}
private int findPosition(int[] inorder, int instart, int inend, int num){
int i;
for(i = instart; i <= inend; i++){
if(inorder[i] == num) return i;
}
return -1;
}
}