重建二叉樹(前序中序,後序中序)
根據前序和中序構建二叉樹:
/**
* Definition for binary tree
* struct TreeNode {
* int val;
* TreeNode *left;
* TreeNode *right;
* TreeNode(int x) : val(x), left(NULL), right(NULL) {}
* };
*/
class Solution {
public:
int index=0;
TreeNode* rebuild(vector<int> pre,vector<int> vin, int left, int right)
{
if(left==right || pre.size()==index)
{
return nullptr;
}
TreeNode *head=NULL;
for(int i=left;i<right; i++)
{
if(pre[index]==vin[i])//查找分界點
{
head=new TreeNode(pre[index]);
index++;
head->left=rebuild(pre, vin, left, i);
head->right=rebuild(pre, vin, i+1, right);
break;
}
}
return head;
}
TreeNode* reConstructBinaryTree(vector<int> pre,vector<int> vin) {
int left=0;
int right=vin.size();
TreeNode* head=rebuild(pre,vin,left,right);
return head;
}
};
根據中序和後序構建二叉樹(注:pre暫爲後序遍歷):
後序pre:[3,4,2,6,7,5,1]
中序vin:[3,2,4,1,6,5,7]
/**
* Definition for binary tree
* struct TreeNode {
* int val;
* TreeNode *left;
* TreeNode *right;
* TreeNode(int x) : val(x), left(NULL), right(NULL) {}
* };
*/
class Solution {
public:
TreeNode* rebuild(vector<int> pre,vector<int> vin, int prel, int prer,int vinl,int vinr)
{
if(left==right)
{
return nullptr;
}
TreeNode *head=NULL;
for(int i=vinl;i<=vinr; i++)
{
if(pre[prer]==vin[i])//查找中序遍歷vin分界點i ,左邊左子樹,右邊右子樹
{
head=new TreeNode(pre[prer]);//構建根節點
head->left=rebuild(pre, vin, prel,i-vinl-1+prel,vinl,i-1);//pre【prel,i-vinl-1+prel】和vin【vinl,i-1】構建左子樹
head->right=rebuild(pre, vin, prel+i-vinl, prer-1,i+1,vinr);//pre【prel+i-vinl, prer-1l】和vin【i+1,vinr】構建左子樹
break;
}
}
return head;
}
TreeNode* reConstructBinaryTree(vector<int> pre,vector<int> vin) {
TreeNode* head=rebuild(pre,vin,0,pre.size()-1,0,vin.size()-1);
return head;
}
};