LeetCode106题：从中序与后序遍历序列构造二叉树

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思路：

 本题的思路与LeetCode105题：从前序与中序遍历序列构造二叉树的思路非常类似。只不过这里要根据后序遍历序列遍历当前节点而已。

class Solution {
    public TreeNode buildTree(int[] inorder, int[] postorder) {
        return helpBuild(inorder,postorder,postorder.length - 1,0,inorder.length);
    }
    public TreeNode helpBuild(int[] in, int[] post, int postIndex, int inFrom, int inTo) {
		if(inFrom >= inTo){
			return null;
		}
		TreeNode root = new TreeNode(post[postIndex]);
		for(int i=inFrom;i<inTo;i++){
			if(in[i] == post[postIndex]){
				root.right = helpBuild(in,post,postIndex - 1,i + 1,inTo);
				root.left = helpBuild(in,post,postIndex - (inTo - i),inFrom,i);
                break;
			}
		}
		return root;
	}
}