重建二叉树
题目描述:
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。
解题思路:详见代码
注意事项:注意错误处理。
/**
* Definition for binary tree
* struct TreeNode {
* int val;
* TreeNode *left;
* TreeNode *right;
* TreeNode(int x) : val(x), left(NULL), right(NULL) {}
* };
*/
class Solution {
public:
TreeNode* reConstructBinaryTree(vector<int> pre,vector<int> vin) {
int preLen = pre.size();
int vinLen = vin.size();
if(preLen == 0 || vinLen == 0 || preLen != vinLen)
return NULL;
int mid = find(vin.begin(), vin.end(), pre[0]) - vin.begin();
if(mid == preLen)
throw std::runtime_error("Invalid input");
vector<int> left_pre(pre.begin()+1, pre.begin()+mid+1);
vector<int> right_pre(pre.begin()+mid+1, pre.end());
vector<int> left_in(vin.begin(), vin.begin()+mid);
vector<int> right_in(vin.begin()+mid+1, vin.end());
if(left_pre.size() != left_in.size() || right_pre.size() != right_in.size())
throw std::runtime_error("Invalid input");
TreeNode* root = new TreeNode(pre[0]);
root->left = reConstructBinaryTree(left_pre, left_in);
root->right = reConstructBinaryTree(right_pre, right_in);
return root;
}
};