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。
class Solution {
public:
TreeNode* reConstructBinaryTree(vector<int> pre,vector<int> vin) {
int pre_len = pre.size();
int in_len = vin.size();
if(pre_len == 0 || in_len == 0 || pre_len != in_len)
return NULL;
TreeNode *head = new TreeNode(pre[0]);//创建根节点
int root_ind = 0;//记录root在中序中的下标
for(int i = 0; i<pre_len; i++){
if(vin[i] == pre[0]){
root_ind = i;
break;
}
}
vector<int> in_left, in_right,pre_left, pre_right;
for(int j = 0; j<root_ind; j++){
in_left.push_back(vin[j]);
pre_left.push_back(pre[j+1]);//第一个为根根节点,跳过
}
for(int j = root_ind+1; j<pre_len; j++){
in_right.push_back(vin[j]);
pre_right.push_back(pre[j]);
}
//递归
head->right = reConstructBinaryTree(pre_right, in_right);
head->left = reConstructBinaryTree(pre_left, in_left);
return head;
}
};