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91 changes: 91 additions & 0 deletions Algorithms/CountingInversionProblem.java
Original file line number Diff line number Diff line change
@@ -0,0 +1,91 @@
import java.util.Scanner;

public class CountingInversionProblem {

public static void main(String[] args) {
Scanner sc = new Scanner(System.in);
System.out.println("Enter the no. of elements : ");
int n = sc.nextInt();

System.out.println("Enter " + n + " integers");
int[] numbers = new int[n];
for (int i = 0; i < n; i++) {

numbers[i] = sc.nextInt();
}
System.out.println("Given Array is ");
printArray(numbers);

int totalInversions = countingInversionUsingMergeSort(numbers, 0, n - 1);
System.out.println("No. Of Inversions are : " + totalInversions);

}

static void printArray(int arr[]) {
int n = arr.length;
for (int i = 0; i < n; ++i)
System.out.print(arr[i] + " ");
System.out.println();
}

static int countingInversionUsingMergeSort(int arr[], int l, int r) {
int inversionCount = 0;
if (l < r) {
int m = (l + r) / 2;

inversionCount = countingInversionUsingMergeSort(arr, l, m);
inversionCount = inversionCount + countingInversionUsingMergeSort(arr, m + 1, r);
inversionCount = inversionCount + merge(arr, l, m, r);

}
return inversionCount;
}

static int merge(int arr[], int l, int m, int r) {
int count = 0;
int n1 = m - l + 1;
int n2 = r - m;
int L[] = new int[n1];
int R[] = new int[n2];

for (int i = 0; i < n1; i++) {
L[i] = arr[l + i];
}
for (int i = 0; i < n2; i++) {
R[i] = arr[m + 1 + i];
}

int i = 0, j = 0;
int k = l;
while (i < n1 && j < n2) {
if (L[i] <= R[j]) {
arr[k] = L[i];
i++;

}

else {
arr[k] = R[j];
count = count + (m + 1) - (l + i);
j++;

}
k++;
}

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

while (j < n2) {
arr[k] = R[j];
j++;
k++;
}
return count;

}

}
61 changes: 61 additions & 0 deletions Algorithms/MaximumSubarrayProblem.java
Original file line number Diff line number Diff line change
@@ -0,0 +1,61 @@
import java.util.*;

public class MaximumSubarrayProblem {

public static void main(String[] args) {
Scanner sc = new Scanner(System.in);
System.out.println("Enter the no. of elements : ");
int n = sc.nextInt();

System.out.println("Enter " + n + " integers");
int[] numbers = new int[n];
for (int i = 0; i < n; i++) {

numbers[i] = sc.nextInt();
}
System.out.println("Given Array is ");
printArray(numbers);

int maxSum = maximumSubArraySum(numbers, 0, n - 1);
System.out.println("Maximum SubArray Sum is : " + maxSum);

}

static void printArray(int arr[]) {
int n = arr.length;
for (int i = 0; i < n; ++i)
System.out.print(arr[i] + " ");
System.out.println();
}

static int maximumSubArraySum(int[] arr, int l, int h) {
if (l == h) {
return arr[l];
}

int m = (l + h) / 2;

return Math.max(maximumCrossingSum(arr, l, m, h),
Math.max(maximumSubArraySum(arr, l, m), maximumSubArraySum(arr, m + 1, h)));
}

static int maximumCrossingSum(int[] arr, int l, int m, int h) {
double negInf = Double.NEGATIVE_INFINITY;
int sum = 0;
int rightSum = (int) negInf;
int leftSum = (int) negInf;
for (int i = m; i >= l; i--) {
sum = sum + arr[i];
if (sum > leftSum)
leftSum = sum;
}
sum = 0;
for (int i = m + 1; i <= h; i++) {
sum = sum + arr[i];
if (sum > rightSum)
rightSum = sum;
}
return Math.max(leftSum + rightSum, Math.max(leftSum, rightSum));

}
}