参考：代码随想录 

class Solution {Map<Integer,Integer> map ;public TreeNode buildTree(int[] inorder, int[] postorder) {map = new HashMap<>();for(int i= 0 ; i < inorder.length; i ++){map.put(inorder[i],i);}return findNode(inorder,0,inorder.length-1,postorder,0,postorder.length-1);}public TreeNode findNode(int[] inorder, int inBegin, int inEnd, int[] postorder, int postBegin, int postEnd){// 左闭右闭的写法if(inBegin > inEnd || postBegin > postEnd){return null;}int rootIndex = map.get(postorder[postEnd]);TreeNode root = new TreeNode(inorder[rootIndex]);int lenOfLeft = rootIndex - inBegin;root.left = findNode(inorder,inBegin,rootIndex-1,postorder,postBegin,postBegin+lenOfLeft-1);root.right = findNode(inorder,rootIndex+1,inEnd,postorder,postBegin+lenOfLeft,postEnd-1);return root;}
}