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。
代码
/**
* Definition for binary tree
* struct TreeNode {
* int val;
* TreeNode *left;
* TreeNode *right;
* TreeNode(int x) : val(x), left(NULL), right(NULL) {}
* };
*/
class Solution {
vector<int> pre, vin;
public:
TreeNode* reConstructBinaryTree(vector<int> pre,vector<int> vin) {
this->pre = pre;
this->vin = vin;
return dfs(0, pre.size() - 1, 0, vin.size() - 1);
}
TreeNode* dfs(int pl, int pr, int vl, int vr) {
if (pl > pr) {
return NULL;
}
TreeNode *root = new TreeNode(pre[pl]);
int vm = vl;
while (vin[vm] != pre[pl]) {
++vm;
}
int len = vm - vl;//计算左子树的个数
root->left = dfs(pl + 1, pl + len, vl, vm - 1);//pl + 1到pl + len是左子树
root->right = dfs(pl + len + 1, pr, vm + 1, vr);//pl + len + 1到pr是右子树
return root;
}
};