leetcode solution 106. construct binary tree from inorder and postorder traversal

 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
class  {
    public TreeNode buildTree(int[] inorder, int[] postorder) {
        if(inorder.length == 0 || postorder.length == 0)
            return null;
        return build(inorder, 0, inorder.length-1, postorder, 0, postorder.length-1);
    }
    public TreeNode build(int[] inorder, int instart, int inend, int[] postorder, int poststart, int postend){
        if(instart>inend || poststart > postend)
            return null;
        TreeNode root = new TreeNode(postorder[postend]);
        int cur = -1;
        for(int i=instart; i<= inend; i++){
            if(root.val == inorder[i]){
                cur = i;
                break;
            }
        }
        root.left = build(inorder, instart, cur-1, postorder, poststart, postend-(inend - cur)-1);
        root.right = build(inorder, cur+1, inend, postorder, postend-(inend - cur), postend-1);
        return root;
    }
}