常见排序算法及其java实现
最近学习了下java，感觉java在基本语法上与C++非常相似。作为练习，我用java实现了冒泡排序、选择排序、插入排序、基尔排序、快速排序、堆排序、计数排序、合并排序。
以下为实现代码：
public class Sort{ public void print_arr(int[] arr){ int len = arr.length; for (int i = 0; i < len; i++){ System.out.print("" + arr[i] + " "); } System.out.println(""); } public int[] dup_arr(int[] arr){ int len = arr.length; int re[] = new int[len]; for (int i = 0; i < len; i++){ re[i] = arr[i]; } return re; } public int[] bubble(int[] arr){ int dup[] = this.dup_arr(arr); int len = dup.length; int tmp = 0; for (int i = 0; i < len; i++){ for (int j = 0; j < len - 1 - i; j++){ if (dup[j] < dup[j+1]){ tmp = dup[j]; dup[j] = dup[j+1]; dup[j+1] = tmp; } } } return dup; } public int[] selection(int[] arr){ int dup[] = this.dup_arr(arr); int len = dup.length; int tmp = 0; int max = 0; for (int i = 0; i < len; i++){ max = i; for (int j = i + 1; j < len; j++){ if (dup[j] > dup[max]){ max = j; } } tmp = dup[i]; dup[i] = dup[max]; dup[max] = tmp; } return dup; } public int[] insertion(int[] arr){ int dup[] = this.dup_arr(arr); for (int i = 1; i < dup.length; i++){ int key = dup[i]; int j = i - 1; while (j >= 0 && dup[j] < key){ dup[j + 1] = dup[j]; j--; } dup[j + 1] = key; } return dup; } public int[] shell(int[] arr, int step){ int dup[] = this.dup_arr(arr); while (step > 0){ //insertion sorting for (int i = step; i < dup.length; i += step){ int j = i - step; int key = dup[i]; while (j >= 0 && dup[j] < key){ dup[j + step] = dup[j]; j -= step; } dup[j + step] = key; } step = step / 2; } return dup; } public void quick(int[] dup, int leftpoint, int rightpoint){ if (leftpoint >= rightpoint){ return; } int key = dup[rightpoint]; int left = leftpoint; int right = rightpoint; while (true){ while (left < right && dup[left] >= key){ left++; } while (left < right && dup[right] <= key){ right--; } int tmp = 0; if (left >= right){ tmp = dup[right]; dup[right] = key; dup[rightpoint] = tmp; break; } tmp = dup[right]; dup[right] = dup[left]; dup[left] = tmp; } this.quick(dup, leftpoint, left - 1); this.quick(dup, left + 1, rightpoint); } //min heap public int micro_adjust(int[] arr, int i, int last){ if (2 * i + 1 > last){ return i; } int max = arr[i] < arr[2 * i + 1] ? i : (2 * i + 1); if (2 * i + 2 > last){ return max; } max = arr[max] < arr[2 * i + 2] ? max : (2 * i + 2); if (max != i){ int tmp = arr[i]; arr[i] = arr[max]; arr[max] = tmp; } return max; } //part of heap sorting. build a min heap public void build_heap(int[] arr, int last){ int mid = (last + 1) / 2 - 1; for (int i = mid; i >= 0; i--){ int tmp = micro_adjust(arr, i, last); //System.out.print("i: " + i + " tmp: " + tmp + "arr: "); //this.print_arr(arr); int flag = i; while (tmp <= mid && tmp != flag){ flag = tmp; tmp = micro_adjust(arr, tmp, last); } } return; } //part of heap sorting. adjust the left arr public void adjust_heap(int[] arr, int last){ int tmp = arr[0]; arr[0] = arr[last]; arr[last] = tmp; this.build_heap(arr, last - 1); return; } //use min heap to sort arr from big to small public int[] heap(int[] arr){ int dup[] = this.dup_arr(arr); this.build_heap(dup, dup.length - 1); for (int i = 0; i < dup.length; i++){ //System.out.print("i: " + i + " arr: "); //this.print_arr(dup); adjust_heap(dup, dup.length - 1 - i); } return dup; } public int[] counting(int[] arr){ int min = arr[0]; int max = arr[0]; for (int i = 1; i < arr.length; i++){ min = min < arr[i] ? min : arr[i]; max = max > arr[i] ? max : arr[i]; } int buckets[] = new int[max - min + 1]; int index = 0; for (int i = 0; i < arr.length; i++){ index = arr[i] - min; buckets[index]++; } int res[] = new int[arr.length]; for (int i = 0; i < res.length; i++){ res[i] = -1; } for (int i = 0; i < arr.length; i++){ index = arr[i] - min; int cnt = 0; for (int j = 0; j < index; j++){ cnt += buckets[j]; } while (res[res.length - 1 - cnt] != -1){ cnt++; } res[res.length - 1 - cnt] = arr[i]; } return res; } /*Failure: don't know how to build the buckets arr ...... public int[] radix(int[] arr){ int dup[] = this.dup_arr(arr); Queue[] buckets = new Queue[10]; for (int i = 0; i < 10; i++){ buckets[i] = new LinkedList(); } int max = dup[0]; for (int i = 1; i < dup.length; i++){ max = max > dup[i] ? max : dup[i]; } int n = 10; while (max > 0){ for (int i = 0; i < dup.length; i++){ buckets[dup[i] % n].add(dup[i]); } int j = 0; for (int i = 0; i < 10; i++){ while (!buckets[i].isEmpty()){ dup[j++] = buckets[i].getFirst(); buckets[i].removeFirst(); } } max /= 10; n *= 10; } return dup; } */ //part of merge sorting: merge two arr together public int[] merge(int[] arr1, int[] arr2){ int res[] = new int[arr1.length + arr2.length]; int i = 0; int j = 0; int k = 0; while (i < arr1.length && j < arr2.length){ if (arr1[i] > arr2[j]){ res[k++] = arr1[i++]; }else{ res[k++] = arr2[j++]; } } while (i < arr1.length){ res[k++] = arr1[i++]; } while (j < arr2.length){ res[k++] = arr2[j++]; } return res; } //the main part of merge_sort public int[] merge_sort(int[] arr, int start, int end){ //System.out.println("start: " + start + " end: " + end); if (end - start < 1){ //System.out.println("end == start"); int tmp[] = {arr[start]}; return tmp; } int flag = (end - start) / 2; int res1[] = merge_sort(arr, start, start + flag); //System.out.println("res1:"); //this.print_arr(res1); int res2[] = merge_sort(arr, start + flag + 1, end); //System.out.println("res2:"); //this.print_arr(res2); int res[] = merge(res1, res2); //this.print_arr(res); return res; } public static void main(String[] args){ int arr[] = {6, 6, 7, 5, 3, 2, 4, 1, 8, 9, 0}; Sort s = new Sort(); System.out.print("The original array: "); s.print_arr(arr); System.out.print("after bubble sorting: "); s.print_arr(s.bubble(arr)); System.out.print("after selection sorting: "); s.print_arr(s.selection(arr)); System.out.print("after insertion sorting: "); s.print_arr(s.insertion(arr)); System.out.print("after shell sorting: "); s.print_arr(s.shell(arr, arr.length/2)); System.out.print("after quick sorting: "); int dup[] = s.dup_arr(arr); s.quick(dup, 0, dup.length - 1); s.print_arr(dup); System.out.print("after heap sorting: "); s.print_arr(s.heap(arr)); System.out.print("after counting sorting: "); s.print_arr(s.counting(arr)); //failure: because don't know how to define buckets //System.out.print("after radix sorting: "); //s.print_arr(s.radix(arr)); //failure: because don't know how to define buckets //System.out.print("after buckets sorting: "); //s.print_arr(s.buckets(arr)); System.out.print("after merge sorting: "); dup = s.dup_arr(arr); s.print_arr(s.merge_sort(dup, 0, dup.length - 1)); } }