[LC 106.从中序与后序遍历序列构造二叉树]

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode() {}
 *     TreeNode(int val) { this.val = val; }
 *     TreeNode(int val, TreeNode left, TreeNode right) {
 *         this.val = val;
 *         this.left = left;
 *         this.right = right;
 *     }
 * }
 */
class Solution {
    public TreeNode buildTree(int[] inorder, int[] postorder) {
        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)
            return null;
        int rootVal = postorder[postEnd];
        int index = 0;
        for(int i = inStart;i <= inEnd;i++){
            if(inorder[i] == rootVal){
                index = i;
                break;
            }
        }
        TreeNode root = new TreeNode(rootVal);
        int leftsize = index-inStart;
        root.left = build(inorder,inStart ,index-1 ,postorder,postStart ,postStart+leftsize-1 );
        root.right = build(inorder,index+1 ,inEnd ,postorder,postStart+leftsize, postEnd-1);
        return root;
    }
}