Java Algorithm Programs

public class LinearSearch {
public static void main(String[] args) {
int[] arr = {10, 20, 30, 40, 50};
int key = 30;
boolean found = false;
for (int i = 0; i < arr.length; i++) {
if (arr[i] == key) {
System.out.println("Element found at index " + i);
found = true;
break;
}
}
if (!found) {
System.out.println("Element not found.");
}
}
}

public class BinarySearchIterative {
public static void main(String[] args) {
int[] arr = {10, 20, 30, 40, 50};
int key = 40;
int result = binarySearch(arr, key);
if (result == -1)
System.out.println("Element not found.");
else
System.out.println("Element found at index " + result);
}
public static int binarySearch(int[] arr, int key) {
int start = 0, end = arr.length - 1;
while (start <= end) {
int mid = (start + end) / 2;
if (arr[mid] == key)
return mid;
else if (arr[mid] < key)
start = mid + 1;
else
end = mid - 1;
}
return -1;
}
}

public class BinarySearchRecursive {
public static void main(String[] args) {
int[] arr = {5, 15, 25, 35, 45};
int key = 15;
int result = binarySearch(arr, 0, arr.length - 1, key);
if (result == -1)
System.out.println("Element not found.");
else
System.out.println("Element found at index " + result);
}
public static int binarySearch(int[] arr, int start, int end, int key) {
if (start > end)
return -1;
int mid = (start + end) / 2;
if (arr[mid] == key)
return mid;
else if (arr[mid] > key)
return binarySearch(arr, start, mid - 1, key);
else
return binarySearch(arr, mid + 1, end, key);
}
}

public class BubbleSort {
public static void main(String[] args) {
int[] arr = {5, 3, 8, 1, 2};
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;
}
}
}
System.out.print("Sorted Array: ");
for (int num : arr) {
System.out.print(num + " ");
}
}
}

public class SelectionSort {
public static void main(String[] args) {
int[] arr = {29, 10, 14, 37, 13};
int n = arr.length;
for (int i = 0; i < n - 1; i++) {
int minIndex = i;
for (int j = i + 1; j < n; j++) {
if (arr[j] < arr[minIndex]) {
minIndex = j;
}
}
// Swap arr[i] and arr[minIndex]
int temp = arr[i];
arr[i] = arr[minIndex];
arr[minIndex] = temp;
}
System.out.print("Sorted Array: ");
for (int num : arr) {
System.out.print(num + " ");
}
}
}

public class InsertionSort {
public static void main(String[] args) {
int[] arr = {9, 7, 5, 3, 1};
int n = arr.length;
for (int i = 1; i < n; i++) {
int key = arr[i];
int j = i - 1;
// Move elements greater than key to one position ahead while (j >= 0 && arr[j] > key) {
arr[j + 1] = arr[j];
j = j - 1;
}
arr[j + 1] = key;
}
System.out.print("Sorted Array: ");
for (int num : arr) {
System.out.print(num + " ");
}
}
}

public class MergeSort {
public static void main(String[] args) {
int[] arr = {12, 11, 13, 5, 6, 7};
mergeSort(arr, 0, arr.length - 1);
System.out.print("Sorted Array: ");
for (int num : arr) {
System.out.print(num + " ");
}
}
static void mergeSort(int[] arr, int left, int right) {
if (left < right) {
int mid = left + (right - left) / 2;
mergeSort(arr, left, mid);
mergeSort(arr, mid + 1, right);
merge(arr, left, mid, right);
}
}
static void merge(int[] arr, int left, int mid, int right) {
int n1 = mid - left + 1;
int n2 = right - mid;
int[] L = new int[n1];
int[] R = new int[n2];
for (int i = 0; i < n1; ++i)
L[i] = arr[left + i];
for (int j = 0; j < n2; ++j)
R[j] = arr[mid + 1 + j];
int i = 0, j = 0, k = left;
while (i < n1 && j < n2) {
if (L[i] <= R[j]) {
arr[k] = L[i];
i++;
} else {
arr[k] = R[j];
j++;
}
k++;
}

while (i < n1) {
arr[k] = L[i];
i++;
k++;
}
while (j < n2) {
arr[k] = R[j];
j++;
k++;
}
}
}

public class QuickSort {
public static void main(String[] args) {
int[] arr = {34, 7, 23, 32, 5, 62};
quickSort(arr, 0, arr.length - 1);
System.out.print("Sorted Array: ");
for (int num : arr) {
System.out.print(num + " ");
}
}
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);
}
}

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++;
int temp = arr[i];
arr[i] = arr[j];
arr[j] = temp;
}
}
int temp = arr[i + 1];
arr[i + 1] = arr[high];
arr[high] = temp;
return i + 1;
}
}

public class CountingSort {
public static void main(String[] args) {
int[] arr = {4, 2, 2, 8, 3, 3, 1};
int max = findMax(arr);
int[] count = new int[max + 1];
int[] output = new int[arr.length];
// Count the occurrences
for (int num : arr) {
count[num]++;
}
// Modify the count array
for (int i = 1; i < count.length; i++) {
count[i] += count[i - 1];
}
// Build the output array
for (int i = arr.length - 1; i >= 0; i--) {
output[count[arr[i]] - 1] = arr[i];
count[arr[i]]--;
}
// Print sorted array
System.out.print("Sorted Array: ");
for (int num : output) {
System.out.print(num + " ");
}
}
static int findMax(int[] arr) {
int max = arr[0];
for (int num : arr) {
if (num > max) {
max = num;
}
}
return max;
}
}

public class HeapSort {
public static void main(String[] args) {
int[] arr = {15, 5, 20, 1, 17, 10, 30};
heapSort(arr);
System.out.print("Sorted Array: ");
for (int num : arr) {
System.out.print(num + " ");
}
}
public static void heapSort(int[] arr) {
int n = arr.length;
// Build max heap
for (int i = n / 2 - 1; i >= 0; i--) {
heapify(arr, n, i);
}
// Extract elements from heap one by one
for (int i = n - 1; i > 0; i--) {
// Swap the root (maximum) with the last element
int temp = arr[0];
arr[0] = arr[i];
arr[i] = temp;
// Call heapify on the reduced heap
heapify(arr, i, 0);
}
}
public static void heapify(int[] arr, int n, int i) {
int largest = i;
int left = 2 * i + 1;
int right = 2 * i + 2;
// If left child is larger than root
if (left < n && arr[left] > arr[largest]) {
largest = left;
}
// If right child is larger than largest so far
if (right < n && arr[right] > arr[largest]) {
largest = right;
}
// If largest is not root
if (largest != i) {
int swap = arr[i];
arr[i] = arr[largest];
arr[largest] = swap;
// Recursively heapify the affected sub-tree
heapify(arr, n, largest);
}
}
}