前序遍历和中序遍历树构造二叉树

 1 /**
 2  * Definition of TreeNode:
 3  * class TreeNode {
 4  * public:
 5  *     int val;
 6  *     TreeNode *left, *right;
 7  *     TreeNode(int val) {
 8  *         this->val = val;
 9  *         this->left = this->right = NULL;
10  *     }
11  * }
12  */
13  
14 
15 class Solution {
16     /**
17      *@param preorder : A list of integers that preorder traversal of a tree
18      *@param inorder : A list of integers that inorder traversal of a tree
19      *@return : Root of a tree
20      */
21 public:
22     TreeNode *buildTree(vector<int> &preorder, vector<int> &inorder) {
23         // write your code here
24         TreeNode *root = NULL;
25         vector<int> preorder_l,preorder_r,inorder_l,inorder_r;
26         int i,root_index=0;
27 
28         if(preorder.empty()!=1 || inorder.empty()!=1) {
29             root = new TreeNode(preorder[0]); //  在前序队列中找根节点
30 
31             //  在中序队列中找出根节点位置
32             for(i=0; i<inorder.size(); i++) {
33                 if(preorder[0] == inorder[i])
34                     break;
35                 root_index++;
36             }
37 
38             //  左右子树的前序、中序队列
39             for(i=0; i<root_index; i++) {
40                 preorder_l.push_back(preorder[i+1]);
41                 inorder_l.push_back(inorder[i]);
42             }
43             for(i=root_index+1; i<inorder.size(); i++)  {
44                 preorder_r.push_back(preorder[i]);
45                 inorder_r.push_back(inorder[i]);
46             }
47 
48             root->left = buildTree(preorder_l, inorder_l);
49             root->right = buildTree(preorder_r, inorder_r);
50         }
51         return root;
52     }
53 };