ConstructBinaryTreeFromInorder&PostOrder.txt

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
 *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
 *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
 * };
 */
class Solution {
public:
    unordered_map<int,int> mp;
    TreeNode* buildTree(vector<int>& inorder, vector<int>& postorder) 
    {
        if(inorder.size()==0 || postorder.size()==0)
            return NULL;
        
        for(int i=0;i<inorder.size();i++)
        {
            mp[inorder[i]]=i;
        }
        return solve(inorder,postorder,0,inorder.size(),0,inorder.size());
    }
    
   // postorder-- left right root 
   //  preorder--  root left right
    
    TreeNode* solve(vector<int> inorder,vector<int> postorder,int i1,int i2,int j1,int j2)
    {
        if(i1>=i2 || j1>=j2)
            return NULL;
        TreeNode* temp=new TreeNode(postorder[j2-1]);
        int indx=mp[temp->val];
        int diff=indx-i1;
        temp->left=solve(inorder,postorder,i1,i1+diff,j1,j1+diff);
        temp->right=solve(inorder,postorder,i1+diff+1,i2,j1+diff,j2-1);
        return temp;
    }
};