【leetcode】105. 从前序与中序遍历序列构造二叉树

 

struct TreeNode* buildTree(int* preorder, int preorderSize, int* inorder, int inorderSize){
    if(preorderSize==0 || inorderSize==0)
        return NULL;
    struct TreeNode** stArr=(struct TreeNode**)calloc(preorderSize,sizeof(struct TreeNode*));
    int top=-1, pPst=0, iPst=0, flag=iPst;
    struct TreeNode* root=(struct TreeNode*)calloc(1,sizeof(struct TreeNode));
    struct TreeNode* temp=root;
    root->val=preorder[pPst++];
    stArr[++top]=root;
    while(pPst<preorderSize && iPst<inorderSize){            
        while(top>=0 && stArr[top]->val == inorder[iPst]){
            temp=stArr[top--];
            iPst++;
        }
        struct TreeNode* node=(struct TreeNode*)calloc(1,sizeof(struct TreeNode));
        node->val=preorder[pPst++];
        stArr[++top]=node;
        if(flag != iPst)
            temp->right=node;
        else
            temp->left=node;
        temp=node;
        flag=iPst;
    }
    return root;
}