重构二叉树

重构二叉树算法流程

表格分析

算法代码

struct TreeNode {
    int val;
    TreeNode *left;
    TreeNode *right;
    TreeNode(int x) : val(x), left(NULL), right(NULL) {}
};

struct TreeNode* ReconstruBTree(vector<int> preTree, vector<int> midTree)
{
    if (preTree.size() == 0 || midTree.size() == 0){
        return nullptr;
    }
    int leftcnt =0,rightcnt= 0,rootIndex=0;
    int rootValue = preTree[0];
    int treecnt = preTree.size();
    bool bFindRoot = false;
    for (int i = 0; i < midTree.size();i++)
    {       
        if (rootValue == midTree[i])
        {           
            bFindRoot = true;
            rootIndex = i;
            break;
        }
        leftcnt++;
    }   
    if (!bFindRoot){ return nullptr;}
    rightcnt = treecnt - leftcnt - 1;

    vector<int>preleftTree;
    vector<int>prerightTree;

    vector<int>midleftTree;
    vector<int>midrightTree;
    for (int i = 0; i < midTree.size(); i++)
    {
        if (i<rootIndex)
        {
            midleftTree.push_back(midTree[i]);
        }
        else if (i>rootIndex){
            midrightTree.push_back(midTree[i]);
        }
    }

    for (int i = 0; i < preTree.size(); i++)
    {
        if (i>0 && i <= leftcnt)
        {
            preleftTree.push_back(preTree[i]);
        }
        else if (i > leftcnt)
        {
            prerightTree.push_back(preTree[i]);
        }
    }

    TreeNode* rootTree = new TreeNode(rootValue);
    TreeNode* lNode = ReconstruBTree(preleftTree, midleftTree);
    TreeNode* rNode = ReconstruBTree(prerightTree, midrightTree);
    rootTree->left = lNode; 
    rootTree->right = rNode;
    return rootTree;    
}