Merge pull request larissalages#18 from gokulkannan7/master

mergesort algorithm in c++

Author: larissalages

classical_algorithms/mergesort.cpp

@@ -0,0 +1,62 @@
+void merge(int a[], int l, int m, int r)
+{
+  int l1 = m - l + 1;
+  int l2 = r - m;
+
+  int temp1[l1];
+  int temp2[l2];
+
+  for (int i = 0; i < l1; i++)
+  {
+    temp1[i] = a[l + i];
+  }
+  for (int j = 0; j < l2; j++)
+  {
+    temp2[j] = a[m + j + 1];
+  }
+  int i = 0;
+  int j = 0;
+  int k = l;
+
+  while (i < l1 && j < l2)
+  {
+    if (temp1[i] < temp2[j])
+    {
+      a[k] = temp1[i];
+      i++;
+    }
+
+    else
+    {
+      a[k] = temp2[j];
+      j++;
+    }
+
+    while (i < l1)
+    {
+      a[k] = temp1[i];
+      i++;
+      k++;
+    }
+
+    while (j < l2)
+    {
+      a[k] = temp2[j];
+      j++;
+      k++;
+    }
+  }
+}
+
+void mergesort(int a[], int l, int r)
+{
+  if (l < r)
+  {
+    int m = r + (l - r) / 2;
+
+    mergesort(a, l, m);
+    mergesort(a, m + 1, r);
+
+    merge(a, l, m, r);
+  }
+}