Leetcode 随笔之 ------ Construct Binary Tree from Inorder and Postorder Traversal

public class Solution {
    
    Map<Integer, Integer> inMap;
    int[] inorder;
    int[] postorder;
    
    public TreeNode buildTree(int[] inorder, int[] postorder) {
        this.inorder = inorder;
        this.postorder = postorder;
        
       
        inMap = new HashMap<Integer, Integer>();
        
       
            for(int j = 0;j < inorder.length;j++) {
                
               
                inMap.put(inorder[j],j);
                
            
        }
        
        int in_start = 0;
        int in_end = inorder.length - 1;
        int po_start = 0;
        int po_end = postorder.length - 1;
        
        return build(in_start, in_end,  po_start,  po_end);
    }
    
    public TreeNode build(int in_start,int in_end, int po_start, int po_end) {
        if(in_end < in_start||po_end < po_start)
            return null;
        
        
        TreeNode root = new TreeNode(postorder[po_end]);
       
        int index_root_inorder = inMap.get(root.val);
        
            
        
        root.left = build(in_start, index_root_inorder - 1, po_start, po_start + index_root_inorder - 1 - in_start );
        root.right = build(index_root_inorder + 1, in_end, po_start + index_root_inorder - in_start, po_end - 1);
        
        return root;
        
    }
}