Question:

Given inorder and postorder traversal of a tree, construct the binary tree.

Note:
You may assume that duplicates do not exist in the tree.

/**
 * 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[] inorder, int[] postorder) {
        if(postorder.length<1) return null;
        return subBuild(inorder,0,inorder.length-1,postorder,0,postorder.length-1);
    }

	private TreeNode subBuild(int[] inorder, int instart, int inend, int[] postorder,
			int poststart, int postend) {
		int root = postorder[postend];
		TreeNode tn = new TreeNode(root);
		if(instart==inend) return tn;
		int index = instart;
		while(inorder[index]!=root){
			index++;
		}
		int leftlen = index-instart-1;
		int rightlen = inend-index-1;
		if(index!=instart){
			tn.left = subBuild(inorder, instart, index-1, postorder, poststart, poststart+leftlen);
		}else {
			tn.left = null;
		}
		if(index!=inend){
			tn.right = subBuild(inorder, index+1, inend, postorder, postend-1-rightlen, postend-1);
		}else {
			tn.right = null;
		}
		return tn;
	}
}

leetcode Construct Binary Tree from Inorder and Postorder Traversal 难度系数3 3.38