105. Construct Binary Tree from Preorder and Inorder Traversal

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
 *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
 *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
 * };
 */
class Solution {
public:
    TreeNode* makeTree(vector<int>&pre, vector<int>&in, int &index, int s , int e)
    {
        if(index==pre.size() || s > e)
        {
            return NULL;
        }

        int mid;

        for(int i = s; i<=e; i++)
        {
            if(in[i] == pre[index])
            {
                mid = i;
                break;
            }
        }

        //creating node
        TreeNode* temp = new TreeNode(pre[index++]);


        temp -> left = makeTree(pre, in, index, s, mid -1);

        temp -> right = makeTree(pre,in, index, mid +1, e);

        return temp; 
    }

    TreeNode* buildTree(vector<int>& preorder, vector<int>& inorder) {
        //to traverse preorder vector
        int i = 0;

        return makeTree(preorder, inorder, i, 0, preorder.size()-1);
    }
};