【leetcode】Construct Binary Tree from Inorder and Postorder Traversal

Given inorder and postorder traversal of a tree, construct the binary tree.

Note:
You may assume that duplicates do not exist in the tree.

 

 

class Solution {
public:
    TreeNode* createTree(vector<int>& inorder,int instart,int inend,vector<int> &postorder,int poststart,int postend)
    {
        if(instart>inend) return NULL;

        int root=postorder[postend];

        int index;

        for(int i=instart;i<=inend;i++)
        {
            if(inorder[i]==root)
            {
                index=i;
                break;
            }
        }

        int len=index-instart;
        TreeNode *left=createTree(inorder,instart,index-1,postorder,poststart,poststart+len-1);
        TreeNode *right=createTree(inorder,index+1,inend,postorder,poststart+len,postend-1);

        TreeNode *node=new TreeNode(root);
        node->left=left;
        node->right=right;

        return node;
    }
    TreeNode* buildTree(vector<int>& inorder, vector<int>& postorder) {
        
        if(inorder.size()==0) return NULL;

        TreeNode *head=createTree(inorder,0,inorder.size()-1,postorder,0,postorder.size()-1);
        return head;
    }
};