Construct Binary Tree from Preorder and Inorder Traversal

已知前序遍历和中序遍历可以得到原二叉树。

/**
 * 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 *buildTree(vector<int> &preorder, vector<int> &inorder) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        if(preorder.size()==0)
        return NULL;
        return build(preorder,inorder,0,preorder.size(),0);
    }
    
    TreeNode *build(vector<int> &preorder, vector<int> &inorder,int p,int t,int i)
    {
        if(t==0)
        return NULL;
        TreeNode* head = (TreeNode *)malloc(sizeof(TreeNode));
        head->val = preorder[p];
        int j = -1;
        for( j = i;j<t+i;j++)
        {
            if(inorder[j] == preorder[p])
            break;
        }
        head->left = build(preorder,inorder,p+1,j-i,i);
        head->right = build(preorder,inorder,p+j-i,t-j-i,j+1);
        return head;
    }
};