Construct Binary Tree from Inorder and Postorder Traversal(根据中序遍历和后序遍历构建二叉树)

根据中序和后续遍历构建二叉树。

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
class Solution {
    public TreeNode buildTree(int[] inorder, int[] postorder) {
        if(inorder==null&&postorder==null||(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>postStart) return null;
        TreeNode root=new TreeNode(postorder[postEnd]); //后续遍历的最后一个是根节点
        //在中序遍历中找到根节点的位置
        int i;
        for( i=inStart;i<=inEnd;i++){
            if(inorder[i]==postorder[postEnd]) break;
        }

        root.left=build(inorder,inStart,i-1,postorder,postStart,postStart+i-inStart-1);
        root.right=build(inorder,i+1,inEnd,postorder,postStart+i-inStart,postEnd-1);
        return root;
    }
}