Lecture 50 :- Find First Repeating Element

To find the first repeating element in an array, you can use a hash map to keep track of the frequency of each element while traversing the array. As soon as you encounter an element with a frequency greater than one, it means it is the first repeating element.

Here's the C++ code to find the first repeating element in an array:

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#include <iostream> #include <vector> #include <unordered_map> int findFirstRepeatingElement(std::vector<int>& nums) {    std::unordered_map<int, int> frequencyMap;    for (int num : nums) {        frequencyMap[num]++;    }    for (int num : nums) {        if (frequencyMap[num] > 1) {            return num;        }    }    return -1; // No repeating element found } int main() {    std::vector<int> nums = {3, 1, 4, 2, 1, 5, 3};    int firstRepeatingElement = findFirstRepeatingElement(nums);    if (firstRepeatingElement != -1) {        std::cout << "First repeating element: " << firstRepeatingElement << std::endl;    } else {        std::cout << "No repeating element found." << std::endl;    }    return 0; }

Example Output:

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First repeating element: 3

In this code, the findFirstRepeatingElement function calculates the frequency of each element using a hash map and then checks for the first repeating element in the array. The time complexity of this approach is O(n), where n is the number of elements in the array.