algorithm-examples/cpp-algorithm/src/hashtable/optimized_lca.h at main · codejsha/algorithm-examples · GitHub

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#ifndef CPP_ALGORITHM_OPTIMIZED_LCA_H
#define CPP_ALGORITHM_OPTIMIZED_LCA_H

#include "binary_tree.h"

#include <stdexcept>
#include <unordered_set>

namespace OptimizedLca
{
    /**
     * \brief Find the lowest common ancestor of two nodes in a binary tree.
     * \details Traverse up node1 and node2 together until they meet.
     * \param node1 the first node
     * \param node2 the second node
     * \return the lowest common ancestor of node1 and node2
     */
    const BinaryTree::ExtendedNode<int>* FindOptimizedLowestCommonAncestor(
        const BinaryTree::ExtendedNode<int>* node1,
        const BinaryTree::ExtendedNode<int>* node2);
}

// ----------------------------------------------------------------------------
inline const BinaryTree::ExtendedNode<int>* OptimizedLca::FindOptimizedLowestCommonAncestor(
    const BinaryTree::ExtendedNode<int>* node1,
    const BinaryTree::ExtendedNode<int>* node2)
{
    auto iter1 = node1;
    auto iter2 = node2;
    std::unordered_set<const BinaryTree::ExtendedNode<int>*> nodes_on_path;

    // traverse up node1 and node2 together until they meet
    while (iter1 != nullptr || iter2 != nullptr)
    {
        if (iter1 != nullptr)
        {
            if (nodes_on_path.contains(iter1))
            {
                return iter1;
            }
            nodes_on_path.insert(iter1);
            iter1 = iter1->parent;
        }
        if (iter2 != nullptr)
        {
            if (nodes_on_path.contains(iter2))
            {
                return iter2;
            }
            nodes_on_path.insert(iter2);
            iter2 = iter2->parent;
        }
    }
    throw std::invalid_argument("No common ancestor found.");
}

#endif