Construct Binary Tree from Inorder and Postorder Traversal

Construct Binary Tree from Inorder and Postorder Traversal

Given inorder and postorder traversal of a tree, construct the binary tree.

Note:
You may assume that duplicates do not exist in the tree.

» Solve this problem

/**
 * 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 &inorder, vector &postorder) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        int end = inorder.size() - 1;
        if (end < 0) return NULL;
        return getRoot(inorder, postorder, 0, end, postorder[end], 0);
    }
    
    TreeNode *getRoot(vector &inorder, vector &postorder,
                 int start, int end, int rootVal, int offset) {
        if (start > end) return NULL;
        
        TreeNode *root = new TreeNode(rootVal);
        
        int rootPosInOrder = start;
        for (; rootPosInOrder < end; ++rootPosInOrder) {
            if (inorder[rootPosInOrder] == rootVal) break;
        }
        
        root->left = getRoot(inorder, postorder, start,
               rootPosInOrder - 1, postorder[rootPosInOrder - 1 + offset], offset);
        root->right = getRoot(inorder, postorder, rootPosInOrder + 1,
              end, postorder[end - 1 + offset], offset - 1);
        return root;
    }
};