剑指offer---重建二叉树

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。

/**
* 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* dfs(vector<int> pre, vector<int> vin, int start1, int end1, int start2, int end2)
{
TreeNode *root = new TreeNode(pre[start1]);

if(start1 == end1)
if(start2 == end2 && pre[start1] == vin[start2])
return root;

// 找到树根
int i = start2;
for(; i<=end2; i++)
if(vin[i] == pre[start1])
break;

int leftlen = i - start2;
if(leftlen > 0)
root->left = dfs(pre, vin, start1+1, start1+leftlen, start2, i-1);
if(leftlen < end1-start1)
root->right = dfs(pre, vin, start1+leftlen+1, end1, i+1, end2);

return root;
}

TreeNode* reConstructBinaryTree(vector<int> pre,vector<int> vin)
{
return dfs(pre, vin, 0, pre.size()-1, 0, vin.size()-1);
}
};