Create aho_corasick.cpp #3027

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	/**
	* @file
	* @brief Aho-Corasick Algorithm[](https://en.wikipedia.org/wiki/Aho%E2%80%93Corasick) - Multi-pattern string search.
	* @details Builds a trie + failure links for O(n + m + z) multi-pattern matching. Inspired by GFG/LeetCode #30.
	* @author [Saurabh Kokate](https://github.com/kokatesaurabh)
	*/
	#include <cassert>
	#include <iostream>
	#include <queue>
	#include <string>
	#include <unordered_map>
	#include <vector>

	namespace strings { namespace aho_corasick {
	// Trie node struct
	struct TrieNode {
	std::unordered_map<char, int> children;
	int fail = 0;
	std::vector<int> output; // Pattern indices ending here
	};

	// Build trie + failure links
	std::vector<TrieNode> buildTrie(const std::vector<std::string>& patterns) {
	// ... (implement: insert patterns, BFS for fails)
	}

	// Search function
	std::vector<std::pair<size_t, size_t>> search(const std::string& text, const std::vector<std::string>& patterns) {
	// ... (implement: traverse text, collect matches via output links)
	return {}; // vector of (text_pos, pattern_index)
	}
	} } // namespace

	static void test() {
	std::vector<std::string> pats = {"he", "she", "his", "hers"};
	std::string text = "ushers";
	auto matches = strings::aho_corasick::search(text, pats);
	assert(matches.size() == 3); // Expected: (0,"ushe"), etc. — adjust asserts
	// More tests: empty, no-match, overlaps.
	std::cout << "All tests passed!\n";
	}

	int main() { test(); return 0; }

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