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/**
* Definition for a binary tree node.
* struct TreeNode {
* int val;
* TreeNode *left;
* TreeNode *right;
* TreeNode(int x) : val(x), left(NULL), right(NULL) {}
* };
*/
class Solution {
public:
TreeNode* buildTree(vector<int>& preorder, vector<int>& inorder) {
return buildSubTree(preorder,inorder,0,preorder.size()-1,0,inorder.size()-1);
}
TreeNode* buildSubTree(vector<int> &preorder, vector<int> &inorder, int pre_left, int pre_right, int in_left, int in_right)
{
if(pre_left > pre_right || in_left > in_right)
return NULL;
else if(pre_left == pre_right || in_left == in_right)
{
TreeNode *new_node = new TreeNode(preorder[pre_left]);
return new_node;
}
else
{
TreeNode *new_node = new TreeNode(preorder[pre_left]);
int i = in_left;
for(; i <= in_right; i++)
{
if(inorder[i] == preorder[pre_left])
break;
}
int new_node_position_in_order = i;
int left_length = new_node_position_in_order-in_left;
new_node->left = buildSubTree(preorder, inorder, pre_left+1, pre_left+left_length, in_left, new_node_position_in_order-1);
new_node->right = buildSubTree(preorder, inorder, pre_left+left_length+1, pre_right, new_node_position_in_order+1,in_right);
return new_node;
}
}
};
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