5.2.1由先序和中序遍历建立二叉树

文章目录

• • 1.题目
  • 2.代码

1.题目

• 题目要求

• 思路：题目要求用先序和中序遍历来建立二叉树。

• eg：

For example, given

preorder = [3,9,20,15,7]
inorder = [9,3,15,20,7]
Return the following binary tree:

    3
   / \
  9  20
    /  \
   15   7

• eg：下面来看一个例子, 某一二叉树的中序和后序遍历分别为：
  

2.代码

class Solution
{
public:
	TreeNode* buildTree(vector<int>& preorder, vector<int>& inorder)
	{
		return SubbuildTree(preorder,0,preorder.size()-1,inorder,0,inorder.size()-1);
	}
	TreeNode* SubbuildTree(vector<int>& preorder, int pleft, int pright,vector<int>& inorder, int ileft, int iright)
	{
		if ((pleft > pright) || (ileft > iright)) return NULL;
		int i=0;
		for (i=ileft;i<iright;++i)
		{
			if (inorder[i] == preorder[pleft])
				break;
		}
		TreeNode* root = new TreeNode(preorder[pleft]);
		root ->left=SubbuildTree(preorder,pleft+1,pleft+i-ileft,inorder,ileft,i-1);
		root ->right=SubbuildTree(preorder,pleft+i-ileft+1,right,inorder,i+1,iright);
	}
	
};