Searching Algorithms

Linear Search

Linear search is the simplest searching algorithm that sequentially checks each element in a list until a match is found or the entire list has been searched.

public class LinearSearch {
    public static int linearSearch(int[] arr, int target) {
        for (int i = 0; i < arr.length; i++) {
            if (arr[i] == target) {
                return i; // Element found at index i
            }
        }
        return -1; // Element not found
    }

    public static void main(String[] args) {
        int[] array = {4, 2, 7, 1, 9, 5};
        int targetElement = 7;
        int result = linearSearch(array, targetElement);

        if (result != -1) {
            System.out.println("Element found at index: " + result);
        } else {
            System.out.println("Element not found in the array.");
        }
    }
}

Time Complexity :

best case: 0(1) -> found at index[0]

worst case: O(n) -> n is size of an array.

Binary Search

Binary search is a more efficient algorithm for sorted arrays. It works by repeatedly dividing the search interval in half.

import java.util.Arrays;

public class BinarySearch {
    public static int binarySearch(int[] arr, int target) {
        int left = 0;
        int right = arr.length - 1;

        while (left <= right) {
            int mid = left + (right - left) / 2;

            if (arr[mid] == target) {
                return mid; // Element found at index mid
            } else if (arr[mid] < target) {
                left = mid + 1;
            } else {
                right = mid - 1;
            }
        }

        return -1; // Element not found
    }

    public static void main(String[] args) {
        int[] array = {1, 2, 4, 5, 7, 9};
        int targetElement = 5;
        int result = binarySearch(array, targetElement);

        if (result != -1) {
            System.out.println("Element found at index: " + result);
        } else {
            System.out.println("Element not found in the array.");
        }
    }
}

Sorting Algorithms

Bubble Sort

Bubble Sort is a simple sorting algorithm that repeatedly steps through the list, compares adjacent elements, and swaps them if they are in the wrong order.

public class BubbleSort {
    public static void bubbleSort(int[] arr) {
        int n = arr.length;

        for (int i = 0; i < n - 1; i++) {
            for (int j = 0; j < n - i - 1; j++) {
                if (arr[j] > arr[j + 1]) {
                    // Swap arr[j] and arr[j+1]
                    int temp = arr[j];
                    arr[j] = arr[j + 1];
                    arr[j + 1] = temp;
                }
            }
        }
    }

    public static void main(String[] args) {
        int[] array = {4, 2, 7, 1, 9, 5};
        bubbleSort(array);
        System.out.println("Sorted array: " + Arrays.toString(array));
    }
}

Quick Sort

Quick Sort is a divide-and-conquer algorithm that works by selecting a 'pivot' element and partitioning the other elements into two sub-arrays.

import java.util.Arrays;

public class QuickSort {
    public static void quickSort(int[] arr, int low, int high) {
        if (low < high) {
            int pi = partition(arr, low, high);

            quickSort(arr, low, pi - 1);
            quickSort(arr, pi + 1, high);
        }
    }

    public static int partition(int[] arr, int low, int high) {
        int pivot = arr[high];
        int i = low - 1;

        for (int j = low; j < high; j++) {
            if (arr[j] < pivot) {
                i++;

                // Swap arr[i] and arr[j]
                int temp = arr[i];
                arr[i] = arr[j];
                arr[j] = temp;
            }
        }

        // Swap arr[i+1] and arr[high] (pivot)
        int temp = arr[i + 1];
        arr[i + 1] = arr[high];
        arr[high] = temp;

        return i + 1;
    }

    public static void main(String[] args) {
        int[] array = {4, 2, 7, 1, 9, 5};
        quickSort(array, 0, array.length - 1);
        System.out.println("Sorted array: " + Arrays.toString(array));
    }
}