力扣第 106 题「 从后序和中序遍历序列构造二叉树」

class Solution {
public:
    unordered_mapfindIndex;
    TreeNode* buildTree(vector& inorder, vector& postorder) {
        for(int i=0;i inorder,int instart,int inend,vector postorder,int postart,int poend){

        if(instart>inend)
        return nullptr;

        int rootval=postorder[poend];
        TreeNode* root=new TreeNode(rootval);
        int index=findIndex[rootval];

        int leftsize=index-instart;
        root->left=build(inorder,instart,index-1, postorder,postart,postart+leftsize-1);
        root->right=build(inorder,index+1,inend,  postorder,postart+leftsize,poend-1);
        return root; 
    }
};