Added Introsort

Author: Anshul-Ji

cpp/sorting/Introsort.cpp

@@ -0,0 +1,145 @@
+#include <bits/stdc++.h>
+using namespace std;
+
+// A utility function to swap the values pointed by
+// the two pointers
+void swapValue(int* a, int* b)
+{
+int* temp = a;
+a = b;
+b = temp;
+return;
+}
+
+/* Function to sort an array using insertion sort*/
+void InsertionSort(int arr[], int* begin, int* end)
+{
+// Get the left and the right index of the subarray
+// to be sorted
+int left = begin - arr;
+int right = end - arr;
+
+for (int i = left + 1; i <= right; i++) {
+int key = arr[i];
+int j = i - 1;
+
+/* Move elements of arr[0..i-1], that are
+greater than key, to one position ahead
+of their current position */
+while (j >= left && arr[j] > key) {
+arr[j + 1] = arr[j];
+j = j - 1;
+}
+arr[j + 1] = key;
+}
+
+return;
+}
+
+// A function to partition the array and return
+// the partition point
+int* Partition(int arr[], int low, int high)
+{
+int pivot = arr[high]; // pivot
+int i = (low - 1); // Index of smaller element
+
+for (int j = low; j <= high - 1; j++) {
+// If current element is smaller than or
+// equal to pivot
+if (arr[j] <= pivot) {
+// increment index of smaller element
+i++;
+
+swap(arr[i], arr[j]);
+}
+}
+swap(arr[i + 1], arr[high]);
+return (arr + i + 1);
+}
+
+// A function that find the middle of the
+// values pointed by the pointers a, b, c
+// and return that pointer
+int* MedianOfThree(int* a, int* b, int* c)
+{
+if (*a < *b && *b < *c)
+return (b);
+
+if (*a < *c && *c <= *b)
+return (c);
+
+if (*b <= *a && *a < *c)
+return (a);
+
+if (*b < *c && *c <= *a)
+return (c);
+
+if (*c <= *a && *a < *b)
+return (a);
+
+if (*c <= *b && *b <= *a)
+return (b);
+}
+
+// A Utility function to perform intro sort
+void IntrosortUtil(int arr[], int* begin, int* end,
+int depthLimit)
+{
+int size = end - begin;
+if (size < 16) {
+InsertionSort(arr, begin, end);
+return;
+}
+
+// If the depth is zero use heapsort
+if (depthLimit == 0) {
+make_heap(begin, end + 1);
+sort_heap(begin, end + 1);
+return;
+}
+
+int* pivot
+= MedianOfThree(begin, begin + size / 2, end);
+
+// Swap the values pointed by the two pointers
+swapValue(pivot, end);
+
+// Perform Quick Sort
+int* partitionPoint
+= Partition(arr, begin - arr, end - arr);
+IntrosortUtil(arr, begin, partitionPoint - 1,
+depthLimit - 1);
+IntrosortUtil(arr, partitionPoint + 1, end,
+depthLimit - 1);
+
+return;
+}
+
+/* Implementation of introsort*/
+void Introsort(int arr[], int* begin, int* end)
+{
+int depthLimit = 2 * log(end - begin);
+
+// Perform a recursive Introsort
+IntrosortUtil(arr, begin, end, depthLimit);
+
+return;
+}
+
+
+void printArray(int arr[], int n)
+{
+for (int i = 0; i < n; i++)
+cout << arr[i] << " \n"[i + 1 == n];
+}
+
+// Driver program 
+int main()
+{
+int arr[] = {10, 84, 97, 97, 16, 86, 94, 46, 19, 42, 33, 45, 36, 6, 1 };
+int n = sizeof(arr) / sizeof(arr[0]);
+Introsort(arr, arr, arr + n - 1);
+printArray(arr, n);
+
+return (0);
+}