【leetcode】Construct Binary Tree from Preorder and Inorder Traversal

/**
* Definition for binary tree
* struct TreeNode {
*     int val;
*     TreeNode *left;
*     TreeNode *right;
*     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
* };
*/
class Solution {
public:

int findInorderLoc(vector<int> &inorder,int target,int inSta,int inEnd)//找到先序的根在中序中的位置
{
for(int i=inSta;i<=inEnd;i++)
{
if(inorder[i]==target)
return i;
}
return inSta;
}

TreeNode *dfs(vector<int> &preorder,int preSta,int preEnd, vector<int> &inorder,int inSta,int inEnd)
{
if(preSta>preEnd||inSta>inEnd)//终端情况
return NULL;
TreeNode *root=new TreeNode(preorder[preSta]);//先序序列的第一个为根

int inorderLoc=findInorderLoc(inorder,root->val,inSta,inEnd);
int len1=inorderLoc-inSta;//左子树的元素个数
int len2=inEnd-inorderLoc;//右子树的元素个数

root->left=dfs(preorder,preSta+1,preSta+len1,inorder,inSta,inSta+len1-1);
root->right=dfs(preorder,preSta+len1+1,preEnd,inorder,inSta+len1+1,inEnd);
}

TreeNode *buildTree(vector<int> &preorder, vector<int> &inorder) {
// Note: The Solution object is instantiated only once and is reused by each test case.
return dfs(preorder,0,preorder.size()-1,inorder,0,inorder.size()-1);
}
};