[LeetCode]Construct Binary Tree from Inorder and Postorder Traversal

原创于 2015-12-29 15:49:05 发布 · 362 阅读

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本文介绍了一种通过中序和后序遍历构建二叉树的方法。利用递归方式确定每个节点的位置，最终构造完整的二叉树结构。

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

递归实现

/**
 * 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>& inorder, vector<int>& postorder) {
        int num = inorder.size();
        if(num == 0)
            return NULL;
        return Recursion(0, num-1, num-1, inorder, postorder );
    }
    TreeNode* Recursion(int Istart,int Iend,int Pend,vector<int>& inorder, vector<int>& postorder){  
        if(Istart>Iend)  
            return NULL;  
        TreeNode* root = new TreeNode(postorder[Pend]); //标记根的位置,特别注意根位置的变化  
        int mid = 0;  
        for(int i=Istart; i<=Iend; ++i){  
            if(inorder[i]==root->val)  
                mid = i;  
        }  
        root->left = Recursion(Istart,mid-1,Pend-1-(Iend-mid),inorder, postorder); //递归指向左右的根  
        root->right = Recursion(mid+1,Iend,Pend-1,inorder,postorder);  
        return root;  
    } 
};