Construct Binary Tree from Preorder and Inorder Traversal.cpp

/**
 * 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) {}
 * };
 */

#include <vector>


using namespace std;



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* buildTree(vector<int>& preorder, vector<int>& inorder)
    {
        return buildTree(preorder, 0, preorder.size() - 1, inorder, 0, inorder.size() - 1);
    }


    TreeNode* buildTree(vector<int> &preorder, int pLeft, int pRight, vector<int> &inorder, int iLeft, int iRight)
    {
        if(pLeft > pRight || iLeft > iRight) return nullptr;
        int i = 0;
        for(i = iLeft; i <= iRight; i++)
        {
            if(preorder[pLeft] == inorder[i]) break;
        }
        TreeNode* cur = new TreeNode(preorder[pLeft]);

        cur->left = buildTree(preorder, pLeft + 1, pLeft + i - iLeft, inorder, iLeft, i - 1);
        cur->right = buildTree(preorder, pLeft + i + 1 - iLeft, pRight, inorder, i + 1, iRight);


        return cur;
    }
};