leetcode-Construct Binary Tree from Preorder and Inorder Traversal

 1 #include <iostream>
 2 #include <vector>
 3 using namespace std;
 4 
 5 struct TreeNode {
 6      int val;
 7      TreeNode *left;
 8      TreeNode *right;
 9      TreeNode(int x) : val(x), left(NULL), right(NULL) {}
10  };
11 
12 class Solution {
13 public:
14     typedef vector<int>::iterator Iter;
15     TreeNode *buildTree(vector<int> &preorder, vector<int> &inorder) {
16         return buildTreeRecur(inorder.begin(),inorder.end(),preorder.begin(),preorder.end());
17     }
18     TreeNode* buildTreeRecur(Iter istart,Iter iend,Iter pstart,Iter pend)
19     {
20         if (istart == iend) return NULL;
21         int rootval = *pstart;
22         Iter iterroot = find(istart,iend,rootval);
23         TreeNode *res = new TreeNode(rootval);//建立根节点
24         res->left = buildTreeRecur(istart,iterroot,pstart+1,pstart+1+(iterroot-istart));
25         res->right = buildTreeRecur(iterroot+1,iend,pstart+1+(iterroot-istart),pend);//vector的end是最后元素还要再下一个！
26         return res;
27     }
28 };
29 
30 void inorderTraversal(TreeNode* root)
31 {
32     if (root == nullptr) return;
33     inorderTraversal(root->left);
34     cout << root->val << " ";
35     inorderTraversal(root->right);
36 }
37 void preorderTraversal(TreeNode* root)
38 {
39     if (root == nullptr) return;
40     cout << root->val << " ";
41     preorderTraversal(root->left);
42     preorderTraversal(root->right);
43 }
44 int main()
45 {
46     Solution s;
47     vector<int> inorder = {2,4,1,5,3};
48     vector<int> preorder = { 1,2, 4,3, 5};
49     TreeNode* root = s.buildTree(preorder,inorder);
50     inorderTraversal(root);
51     cout << endl;
52     preorderTraversal(root);
53     return 0;
54 }