Implemented moore voting algorithm

greedy_algorithms/moore_voting.cpp

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+/**
+ * @file
+ * @brief [Moore's Voting Algorithm](https://en.wikipedia.org/wiki/Boyer%E2%80%93Moore_majority_vote_algorithm)
+ * implementation
+ * @details
+ * Moore's Voting Algorithm is used to find the majority element in an array,
+ * which is the element that appears more than n/2 times, where n is the size of the array.
+ * This algorithm works in O(n) time complexity and O(1) space complexity.
+ *
+ * @author [Ayush Kumar](https://github.com/SuprHUlk)
+ */
+
+#include <cassert>   /// for assert
+#include <iostream>  /// for IO operations
+#include <vector>    /// for std::vector
+
+/**
+ * @namespace
+ * @brief Greedy Algorithms
+ */
+namespace greedy_algorithms {
+/**
+ * @namespace
+ * @brief Functions for Moore's Voting Algorithm implementation
+ */
+namespace moore_voting {
+
+/**
+ * @brief Function to find the candidate for majority element.
+ * This function selects a candidate that could be a majority element.
+ * The candidate may or may not be the actual majority element.
+ * 
+ * @param arr the input array
+ * @return the candidate element for the majority
+ */
+int find_candidate(const std::vector<int>& arr) {
+    int candidate = arr[0];
+    int count = 1;
+    for (size_t i = 1; i < arr.size(); i++) {
+        if (arr[i] == candidate) {
+            count++;
+        } else {
+            count--;
+        }
+        if (count == 0) {
+            candidate = arr[i];
+            count = 1;
+        }
+    }
+    return candidate;
+}
+
+/**
+ * @brief Function to check if the candidate is the majority element.
+ * After a candidate is selected, this function verifies whether it is 
+ * actually the majority element by counting its occurrences.
+ * 
+ * @param arr the input array
+ * @param candidate the candidate to check
+ * @return true if the candidate is the majority, false otherwise
+ */
+bool is_majority(const std::vector<int>& arr, int candidate) {
+    int count = 0;
+    for (int num : arr) {
+        if (num == candidate) {
+            count++;
+        }
+    }
+    return count > arr.size() / 2;
+}
+
+/**
+ * @brief Main function to find the majority element using Moore's Voting Algorithm.
+ * This function finds and returns the majority element if it exists, otherwise it returns -1.
+ * 
+ * @param arr the input array
+ * @return the majority element or -1 if no majority element exists
+ */
+int moore_voting_algorithm(const std::vector<int>& arr) {
+    int candidate = find_candidate(arr);
+    if (is_majority(arr, candidate)) {
+        return candidate;
+    } else {
+        return -1;  // No majority element found
+    }
+}
+}  // namespace moore_voting
+}  // namespace greedy_algorithms
+
+/**
+ * @brief Self-test implementations
+ * @returns void
+ */
+static void tests() {
+    std::vector<int> test1 = {2, 2, 1, 1, 1, 2, 2};
+    assert(greedy_algorithms::moore_voting::moore_voting_algorithm(test1) == 2);
+
+    std::vector<int> test2 = {3, 3, 4, 2, 4, 4, 2, 4, 4};
+    assert(greedy_algorithms::moore_voting::moore_voting_algorithm(test2) == 4);
+
+    std::vector<int> test3 = {3, 1, 3, 3, 2};
+    assert(greedy_algorithms::moore_voting::moore_voting_algorithm(test3) == 3);
+
+    std::vector<int> test4 = {1, 2, 3, 4};
+    assert(greedy_algorithms::moore_voting::moore_voting_algorithm(test4) == -1);
+
+    std::cout << "All tests have successfully passed!\n";
+}
+
+/**
+ * @brief Main function
+ * @returns 0 on exit
+ */
+int main() {
+    tests();  // run self-test implementations
+    return 0;
+}