Recently I systematicall review some sorting algorithms, including insertion sort, bubble sort, merge sort and quick sort. I then implement them in C++. All the function takes in a vector<int>& type and directly operates on the input. To use the following code, you need to add the following code to your headers.
1 #include <iostream> 2 #include <vector> 3 #include <ctime> // for randomization in quicksort 4 5 using namespace std;
Insertion Sort:
1 // Insertion sort 2 void insertionSort(vector<int>& arr) { 3 for (int j = 1; j < (signed)arr.size(); j++) 4 for (int i = j - 1; i >= 0 && arr[i] > arr[i + 1]; i--) 5 swap(arr[i], arr[i + 1]); 6 }
Bubble Sort:
1 // Bubble sort 2 void bubbleSort(vector<int>& arr) { 3 for (int i = 0; i < (signed)arr.size() - 1; i++) 4 for (int j = i + 1; j < (signed)arr.size(); j++) 5 if (arr[i] > arr[j]) swap(arr[i], arr[j]); 6 }
Merge Sort:
1 // Merge sort 2 void merge(vector<int>& arr, int left, int mid, int right) { 3 if (left >= right) return; 4 vector<int> larr(arr.begin() + left, arr.begin() + mid + 1); 5 vector<int> rarr(arr.begin() + mid + 1, arr.begin() + right + 1); 6 int i = 0, j = 0, pos = left; 7 while(i < (signed)larr.size() && j < (signed)rarr.size()) { 8 if (larr[i] > rarr[j]) arr[pos++] = rarr[j++]; 9 else arr[pos++] = larr[i++]; 10 } 11 while (i < (signed)larr.size()) arr[pos++] = larr[i++]; 12 while (j < (signed)rarr.size()) arr[pos++] = rarr[j++]; 13 } 14 15 void mergeSortHelper(vector<int>& arr, int left, int right) { 16 if (left >= right) return; 17 int mid = (left + right) / 2; 18 mergeSortHelper(arr, left, mid); 19 mergeSortHelper(arr, mid + 1, right); 20 merge(arr, left, mid, right); 21 } 22 23 void mergeSort(vector<int>& arr) { 24 mergeSortHelper(arr, 0, arr.size() - 1); 25 }
Quicksort:
1 // Quicksort 2 int partition(vector<int>& arr, int left, int right) { 3 // Introduce randomization 4 srand((unsigned)time(0)); 5 int rndIdx = rand() % (right - left + 1) + left; 6 swap(arr[rndIdx], arr[left]); 7 int l = left + 1, r = right; 8 while (l <= r) { 9 if (arr[l] > arr[left] && arr[r] < arr[left]) 10 swap(arr[l], arr[r]); 11 if (arr[l] <= arr[left]) l++; 12 if (arr[r] >= arr[left]) r--; 13 } 14 swap(arr[left], arr[r]); 15 return r; 16 } 17 18 void quickSortHelper(vector<int> &arr, int left, int right) { 19 if (left >= right) return; 20 int pivot = partition(arr, left, right); 21 quickSortHelper(arr, left, pivot - 1); 22 quickSortHelper(arr, pivot + 1, right); 23 } 24 25 void quickSort(vector<int>& arr) { 26 quickSortHelper(arr, 0, arr.size() - 1); 27 }
Welcome for any question, comment and suggestion about the code!