Merge pull request #68 from TORRYNN/Divide

Completed Divide and Conqueror

Author: TORRYNN

25_Divide and Conquer/PracticeQs2.java

@@ -4,7 +4,7 @@ public class PracticeQs2 {
  // largest count.
  // Time Complexity:O(n2);
  public static int MajorityElement(int[] nums) {
- // We know that majorit count we be more than half of the element.
+ // We know that majority count we be more than half of the element.
  int majoritycount = nums.length / 2;
 
  for (int i = 0; i < nums.length; i++) {
@@ -55,7 +55,7 @@ public static int majoritElementCount(int[] numbers, int low, int high) {
  }
 
  public static void main(String[] args) {
- int nums[] = { 2, 2, 1, 1, 1, 1, 1, 2, 2 };
+ int nums[] = { 2, 2, 1, 1, 1, 1, 1, 3, 7 };
  System.out.println(MajorityElement(nums));
  System.out.println(majoritElementCount(nums, 0, nums.length - 1));
  }

25_Divide and Conquer/PracticeQs3.class

@@ -0,0 +1,78 @@
+// InversionCount
+public class PracticeQs3 {
+ // Brute Force Approach
+ // Time Complexity: O(n^2)
+ public static int InversionCount(int arr[], int low, int high) {
+ int count = 0;
+ for (int i = 0; i < high; i++) {
+ for (int j = i + 1; j < high; j++) {
+ if (arr[i] > arr[j] && i < j) {
+ count++;
+ }
+ }
+ }
+ return count;
+
+ }
+ // Using Divide and Conqueror Technique
+ // Time Complexity:O(nlogn)
+ // Modified MergeSort
+ public static int MergeSort(int arr[], int low, int high) {
+
+ int InversionCount = 0;
+ if (low >= high) {
+ return 0;
+ }
+
+ int mid = low + (high - low) / 2;
+ InversionCount = MergeSort(arr, low, mid);
+ InversionCount += MergeSort(arr, mid + 1, high);
+ InversionCount += Merge(arr, low, mid, high);
+
+ return InversionCount;
+ }
+
+ private static int Merge(int arr[], int low, int mid, int high) {
+ int temp[] = new int[high - low + 1];
+ int InversionCount = 0;
+ int i = low;
+ int j = mid + 1;
+ int k = 0;
+
+ while (i <= mid && j <= high) {
+ if (arr[i] <= arr[j]) {
+ temp[k] = arr[i];
+ i++;
+ } else {
+ temp[k] = arr[j];
+ InversionCount += (mid - i+1);
+ j++;
+ }
+ k++;
+
+ }
+ // if there is some remaining element in left part or high part
+ while (i <= mid) {
+ temp[k] = arr[i];
+ k++;
+ i++;
+ }
+ while (j <= high) {
+ temp[k] = arr[j];
+ k++;
+ j++;
+ }
+ for (i = low, k = 0; i <= high; i++, k++) {
+ arr[i] = temp[k];
+ }
+
+ return InversionCount;
+
+ }
+
+ public static void main(String[] args) {
+ int nums[] = { 2, 4, 1, 3, 5 };
+ System.out.println(InversionCount(nums, 0, nums.length - 1));
+ System.out.println(MergeSort(nums, 0, nums.length - 1));
+ }
+}

25_Divide and Conquer/PracticeQs3.java

@@ -0,0 +1 @@
+8