leet-code-105. 從前序與中序遍歷序列構造二叉樹 and leet-code-106 從中序與後序遍歷序列構造二叉樹

leet-code-105. 從前序與中序遍歷序列構造二叉樹:

class Solution {
private:
    int search(int *inorder,int len,int target){
        for(size_t i=0;i<len;++i){
            if(target==inorder[i])
                return i;
        }
        return -1;
    }
    TreeNode* build(int* pre,int *in,int len){
        if(len<=0)
            return NULL;
        TreeNode* root=new TreeNode(pre[0]);
        int len1=search(in,len,pre[0]);
        root->left=build(pre+1,in,len1);
        root->right=build(pre+len1+1,in+len1+1,len-len1-1);
        return root;
    }
public:
    TreeNode* buildTree(vector<int>& preorder, vector<int>& inorder) {
          int *PreOrder=new int [preorder.size()];
          int *InOrder=new int[inorder.size()];
         for(size_t i=0;i<inorder.size();++i){
             InOrder[i]=inorder[i];
             PreOrder[i]=preorder[i];
         }
        TreeNode* root=build(PreOrder,InOrder,inorder.size());
        delete []InOrder;
        delete []PreOrder;
        return root;
    }
};

106. 從中序與後序遍歷序列構造二叉樹:

思路同上：

class Solution {
private:
    int search(int *inorder,int len,int target){
        for(size_t i=0;i<len;++i){
            if(target==inorder[i])
                return i;
        }
        return -1;
    }
private:
    TreeNode* build(int *post,int *in,int len){
        if(len<=0)
            return NULL;
        TreeNode* root=new TreeNode(post[len-1]);
        int len1=search(in,len,post[len-1]);
        root->left=build(post,in,len1);
        root->right=build(post+len1,in+len1+1,len-len1-1);
        return root;
    }
    
public:
    TreeNode* buildTree(vector<int>& inorder, vector<int>& postorder) {
         int *InOrder=new int [inorder.size()];
         int *PostOrder=new int[postorder.size()];
         for(size_t i=0;i<inorder.size();++i){
             InOrder[i]=inorder[i];
             PostOrder[i]=postorder[i];
         }
        TreeNode* root=build(PostOrder,InOrder,inorder.size());
        delete []InOrder;
        delete []PostOrder;
        return root;
    }
};