construct-binary-tree-from-preorder-and-inorder-traversal

题目：

Given preorder and inorder traversal of a tree, construct the binary tree.
Note:
You may assume that duplicates do not exist in the tree

程序：

class Solution {
public:
    TreeNode *buildTree(vector<int> &preorder, vector<int> &inorder) {
        return build(preorder,inorder,0,preorder.size()-1,0,preorder.size()-1);
    }
    TreeNode *build(vector<int> &preorder,vector<int> &inorder,int l1,int r1,int l2,int r2)
    {
        if(l1 > r1)
            return NULL;
        int i,count=0,R = preorder[l1];
        for(i=l2;i<=r2 && inorder[i]!=R;i++)
            count++;
        TreeNode *root = (TreeNode *)malloc(sizeof(TreeNode));
        root->val = R;
        root->left = build(preorder,inorder,l1+1,l1+count,l2,i-1);
        root->right = build(preorder,inorder,l1+1+count,r1,i+1,r2);
        return root;
    }
};