重建二叉树

Desicription

输入某二叉树的前序遍历和中序遍历的结果,请重建出该二叉树。假设输入的前序遍历和中序遍历的结果中都不含重复的数字。例如输入前序遍历序列{1,2,4,7,3,5,6,8}和中序遍历序列{4,7,2,1,5,3,8,6},则重建二叉树并返回。

Solution

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/**
* Definition for binary tree
* struct TreeNode {
* int val;
* TreeNode *left;
* TreeNode *right;
* TreeNode(int x) : val(x), left(NULL), right(NULL) {}
* };
*/
class Solution {
private:
TreeNode* Handle(int midOrderLeft, int midOrderRight, int preOrderLeft, TreeNode* root, const vector<int>& pre, const vector<int>& mid) {
for(int index = midOrderLeft; index <= midOrderRight; index++) {
if(mid[index] == pre[preOrderLeft]) {
root = new TreeNode(mid[index]);
root->left = Handle(midOrderLeft, index - 1, preOrderLeft + 1, root->left, pre, mid);
root->right = Handle(index + 1, midOrderRight, index - midOrderLeft + preOrderLeft + 1, root->right, pre, mid);
return root;
}
}
return nullptr;
}
public:
TreeNode* reConstructBinaryTree(const vector<int>& pre, const vector<int>& mid) {
return Handle(0, mid.size() - 1, 0, nullptr, pre, mid);
}
};