Merge pull request #590 from zachboemer/master

c++ implemetation of merge sort

Author: probot-auto-merge[bot]

C++/mergeSort.cpp

@@ -0,0 +1,118 @@
+#include <iostream>
+using namespace std;
+  
+// Merges two sorted subarrays of A[]. 
+// First sorted subarray is A[l..m].
+// Second sorted subarray is A[m+1..r].
+// You might want to call this function in function mergeSort().
+void merge(int A[], int l, int m, int r) 
+{ 
+	int i = 0;		// cursor in leftArray[]
+	int j = 0;		// cursor in rightArray[]
+	int k = l;		// cursor in A[]
+
+	int sizeOfRight = r - m;	// calculates sizes of subarrays
+	int sizeOfLeft = m - l + 1;
+
+	int leftArray[sizeOfLeft];		// creates temporary arrays
+	int rightArray[sizeOfRight];
+
+	for (i; i < sizeOfLeft; i++) {		// fills leftArray[]
+		leftArray[i] = A[k];
+		k++;
+	}
+
+	for (j; j < sizeOfRight; j++) {		// fills rightAray[]
+		rightArray[j] = A[k];
+		k++;
+	}
+
+	i = 0;	// reseting cursors
+	j = 0;
+	k = l;
+
+	// merging contents of arrays
+	while (i < sizeOfLeft && j < sizeOfRight) { 
+		if (leftArray[i] <= rightArray[j]) {
+			A[k] = leftArray[i];
+			i++;
+			k++;
+		}
+		else {
+			A[k] = rightArray[j];
+			j++;
+			k++;
+		}
+	}
+	
+	// finishes merging the remaining array
+	while (i < sizeOfLeft) {
+		A[k] = leftArray[i];
+		i++;
+		k++;
+	}
+
+	while (j < sizeOfRight) {
+		A[k] = rightArray[j];
+		j++;
+		k++;
+	}
+} 
+
+// using mergeSort to sort sub-array A[l..r]  
+// l is for left index and r is right index of the 
+// sub-array of A[] to be sorted
+void mergeSort(int A[], int l, int r) 
+{ 
+	int first = l;
+	int last = r;
+
+	if (first == last)		// base case
+		return;
+	else {
+		int middle = (first + last) / 2;	// general case
+
+		mergeSort(A,first, middle);
+		mergeSort(A, middle + 1, last);
+
+		merge(A, first, middle, last);
+	}
+}
+
+int main() 
+{ 
+    cout << "Please enter the length (number of elements) of the input array: ";
+	int n;
+	cin >> n;
+	
+	if(n <= 0) {
+		cout << "Illegal input array length!" << endl;
+		return 0;
+	}
+	
+	int* A = new int [n];
+	
+	cout << "Please enter each element in the array" << endl; 
+	cout << "(each element must be an integer within the range of int type)." << endl;
+	for(int i=0; i<n; i++) {
+		cout << "A[" << i << "] = ";
+		cin >> A[i];
+	}
+  
+    cout << "Given array A[] is: "; 
+	for(int i=0; i<n-1; i++)
+		cout << A[i] << ",";
+	cout << A[n-1] << endl;
+	
+  
+    mergeSort(A, 0, n-1);
+  
+    cout << "After mergeSort, sorted array A[] is: "; 
+	for(int i=0; i<n-1; i++)
+		cout << A[i] << ",";
+	cout << A[n-1] << endl;
+	
+	
+	delete [] A;
+    return 0; 
+}