[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.

 

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/**
 * Definition for binary tree
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    TreeNode *DFS(vector<int> &inorder, vector<int> &postorder,int leftstart,int leftend,int rightstart,int rightend)
    {
        if(leftend<leftstart||rightend<rightend) return NULL;
        TreeNode *root=new TreeNode(postorder[rightend]); //
        int pos;
        for(int i=leftstart;i<=leftend;i++)
        {
            if(inorder[i]==postorder[rightend])
            {
                pos=i;
                break;
            }
        }
        int len=pos-leftstart;
        root->left=DFS(inorder,postorder,leftstart,pos-1,rightstart,rightstart+len-1);
        root->right=DFS(inorder,postorder,pos+1,leftend,rightstart+len,rightend-1);
        return root;
    }
    TreeNode *buildTree(vector<int> &inorder, vector<int> &postorder) {
        return DFS(inorder,postorder,0,inorder.size()-1,0,postorder.size()-1);
    }
};