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[leetcode] Construct Binary Tree from Preorder and Inorder Traversal
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.
思路：
由先序遍历和中序遍历确定二叉树的结构。还是那个问题，index-l+i+1是我试出来的，具体为什么需要好好想想。
题解：
/** * Definition for binary tree * struct TreeNode { * int val; * TreeNode *left; * TreeNode *right; * TreeNode(int x) : val(x), left(NULL), right(NULL) {} * }; */class Solution {public: void build(vector<int> &preorder, vector<int> &inorder, int l, int r, int index, TreeNode *&root) { if(l>r) return; root = new TreeNode(preorder[index]); int i; for(i=l;i<=r;i++) if(inorder[i]==preorder[index]) break; build(preorder, inorder, l, i-1, index+1, root->left); build(preorder, inorder, i+1, r, index-l+i+1, root->right); } TreeNode *buildTree(vector<int> &preorder, vector<int> &inorder) { if(preorder.size()==0) return NULL; TreeNode *root; build(preorder, inorder, 0, inorder.size()-1, 0, root); return root; }};
[leetcode] Construct Binary Tree from Preorder and Inorder Traversal
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