Initial commit

cpp/programs/sort_merge.cpp

@@ -0,0 +1,92 @@
+#include <iostream>
+using namespace std;
+
+void merge(int array[], int left, int mid, int right) {
+	int leftArrLen = mid - left + 1;
+	int rightArrLen = right - mid;
+  
+	// Create temp arrays
+	int leftArray[leftArrLen];
+	int rightArray[rightArrLen];
+
+	// Copy data to temp arrays leftArray[] and rightArray[]
+	for (int i = 0; i < leftArrLen; i++) {
+		leftArray[i] = array[left + i];
+	}
+
+	for (auto i = 0; i < rightArrLen; i++) {
+		rightArray[i] = array[mid + 1 + i];
+	}
+  
+	int leftArrIndex = 0; // Initial index of first sub-array
+	int rightArrIndex = 0; // Initial index of second sub-array
+	int mergedArrIndex = left; // Initial index of merged array
+  
+	// Merge the temp arrays back into array[left..right]
+	while (leftArrIndex < leftArrLen && rightArrIndex < rightArrLen) {
+		// Choose one of the two elements at current positions of left and right arrays
+		if (leftArray[leftArrIndex] <= rightArray[rightArrIndex]) {
+			array[mergedArrIndex] = leftArray[leftArrIndex];
+			leftArrIndex++;
+		} else {
+			array[mergedArrIndex] = rightArray[rightArrIndex];
+			rightArrIndex++;
+		}
+		mergedArrIndex++;
+	}
+
+	// Copy the remaining elements of
+	// left[], if there are any
+	while (leftArrIndex < leftArrLen) {
+		array[mergedArrIndex] = leftArray[leftArrIndex];
+		leftArrIndex++;
+		mergedArrIndex++;
+	}
+
+	// Copy the remaining elements of
+	// right[], if there are any
+	while (rightArrIndex < rightArrLen) {
+		array[mergedArrIndex] = rightArray[rightArrIndex];
+		rightArrIndex++;
+		mergedArrIndex++;
+	}
+}
+
+
+void mergeSort(int arr[], int left, int right) {
+	if (left >= right) {
+		return;
+	}
+
+	int middle = (left + right) / 2;
+	mergeSort(arr, left, middle);
+	mergeSort(arr, middle + 1, right);
+	merge(arr, left, middle, right);
+}
+
+// 4 1 3 5 2
+// 4 1 3 5 2 [4, 1] [3]
+// 4 1 3 5 2 [^1, 4] [^3]
+// 1 1 3 5 2 [1, ^4] [^3]
+// 1 3 3 5 2 [1, ^4] [3]^
+// 1 3 4 5 2 [^5] [^2]
+// 1 3 4 2 2 [^5] [2]^
+// 1 3 4 2 5
+
+
+
+int main() {
+	int N = 50;
+	int arr[N];
+	for (int i = 0; i < N; i++) {
+		arr[i] = N - i;
+	}
+
+	mergeSort(arr, 0, N - 1);
+
+	for (int i = 0; i < N; i++) {
+		cout << arr[i] << " ";
+	}
+	cout << endl;
+	return 0;
+}