LeetCode Construct Binary Tree from Preorder and Inorder Tra

Construct Binary Tree from Preorder and Inorder Traversal

Given preorder and inorder traversal of a tree, construct the binary tree.

Note:
You may assume that duplicates do not exist in the tree.

一個小小的下標沒搞好，居然要浪費差不多一個小時，心痛啊。

中序遍歷序列和後序遍歷序列的偏移位置都需要仔細設計好。

class Solution {
public:
	TreeNode *buildTree(vector &preorder, vector &inorder) 
	{
		return conTree(preorder, inorder, 0, preorder.size()-1, 0, inorder.size()-1);
	}

	TreeNode *conTree(vector &preo, vector &ino, 
		int prel, int prer, int inl, int inr)
	{
		if (prel > prer) return NULL;
		TreeNode *t = new TreeNode(preo[prel]);
		auto it = find(ino.begin()+inl, ino.begin()+inr+1, preo[prel]);
		int offset = it-ino.begin()-inl;
		
		//注意：切記，下標如何定位要清楚，是offset還是絕對位置不能搞混了！
		t->left = conTree(preo, ino, prel+1, prel+offset, inl, inl+offset-1);
		t->right = conTree(preo, ino, prel+offset+1, prer, inl+offset+1, inr);
		return t;
	}
};