leetcode Construct Binary Tree from Preorder and Inorder Traversal

最新推荐文章于 2024-01-17 14:50:43 发布

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本文详细介绍了如何使用后序和中序遍历的序列来构建二叉树，通过递归的方法解析序列并创建树结构。

方法类似Construct Binary Tree from Postorder and Inorder Traversal http://blog.youkuaiyun.com/menyangyang/article/details/38686975

代码

class Solution
{
public:
	TreeNode *buildTree(vector<int> &preorder, vector<int> &inorder)
	{
		TreeNode *head = NULL;
		int inSize = inorder.size();
		int preSize = preorder.size();
		if(inSize!=preSize||inSize==0)
			return head;

		return buildTreeHelper(inorder, 0, inSize-1, preorder, 0, preSize-1);

        
    }


	TreeNode * buildTreeHelper(vector<int> &inorder,int start0, int end0 ,vector<int> &preorder,int start1, int end1)
	{
		if(start0>end0||start1>end1)
			return NULL;

		TreeNode *node = new TreeNode(preorder[start1]);

		int leftNum = 0;
		int mid;
		for(int i = start0; i <= end0; ++i)
		{			
			if(inorder[i]==node->val)
			{
			    mid = i;
				break;
			}
		}

        leftNum = mid - start0;
		node->left = buildTreeHelper(inorder,start0, mid-1 ,preorder, start1+1, start1+leftNum);
		node->right = buildTreeHelper(inorder,mid+1, end0, preorder, start1+leftNum+1, end1);

		return node;

	}

};