LeetCode 106. 從中序與後序遍歷序列構造二叉樹（二叉樹基礎之樹的重建）

從中序與後序遍歷序列構造二叉樹

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    TreeNode* buildTree(vector<int>& inorder, vector<int>& postorder) {
        int n = inorder.size();
        return create(0,n-1,0,n-1,inorder,postorder);
    }
    TreeNode* create(int postL,int postR,int inL,int inR,vector<int>& inorder, vector<int>& postorder){
        if(postL>postR){
            return nullptr;
        }
        TreeNode* root = new TreeNode(postorder[postR]); 
        int idx = 0;
        for(int i = inL;i<=inR;i++){
            if(inorder[i]==postorder[postR]){
                idx = i;
                break;
            }
        }
        int numLeft = idx-inL;
        root->left = create(postL,postL+numLeft-1,inL,idx-1,inorder,postorder);
        root->right = create(postL+numLeft,postR-1,idx+1,inR,inorder,postorder);
        return root;
    }
};