105. Construct Binary Tree from Preorder and Inorder Traversal

package Recursion;

public class BuildTree_105 {
	public class TreeNode {
		int val;
		TreeNode left;
		TreeNode right;

		TreeNode(int x) {
			val = x;
		}
	}

	// 105. Construct Binary Tree from Preorder and Inorder Traversal
	public TreeNode buildTree(int[] preorder, int[] inorder) {
		return recur(preorder,0,preorder.length-1,inorder,0,inorder.length-1);

	}
	private TreeNode recur(int[] preorder,int pStart,int pEnd,int[] inorder,int iStart,int iEnd){
		// 遞歸結束條件
		while(pStart>pEnd||iStart>iEnd) {
			return null;
		}
		
		TreeNode treeNode=new TreeNode(preorder[pStart]);
		int index=0;
		while(inorder[iStart+index]!=preorder[pStart]) {
			index++;
		}
		
		treeNode.left=recur(preorder,pStart+1,pStart+index,inorder,iStart,iStart+index-1);
		treeNode.right=recur(preorder,pStart+index+1,pEnd,inorder,iStart+index+1,iEnd);
		
		
		return treeNode;
	}

}