Leetcode 105 Solution

This article provides solution to leetcode question 105 (construct-binary-tree-from-preorder-and-inorder-traversal)
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https://leetcode.com/problems/construct-binary-tree-from-preorder-and-inorder-traversal

Solution

/**
 * Definition for a binary tree node.
 * 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, int l1, int r1, vector<int>& inorder, int l2, int r2) {
        if (l1 > r1 || l2 > r2)
            return NULL;

        int root_val = preorder[l1];
        TreeNode* node = new TreeNode(root_val);

        int pos = l2;
        for (; pos <= r2; pos++)
            if (inorder[pos] == root_val)
                break;

        node->left = buildTree(preorder, l1 + 1, l1 + 1 + pos - l2 - 1, inorder, l2, pos - 1);
        node->right = buildTree(preorder, l1 + 1 + pos - l2, r1, inorder, pos + 1, r2);

        return node;
    }

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