算法实例

Posted 2020-07-02 温故余学

[冒泡排序算法]、[选择排序算法]

 1         /**
 2          * @Description:<p>冒泡排序算法实现</p>
 3          * @time:2016/03/29 下午14:40
 4          */
 5         public static void bubbleSort(int[] arr) {
 6            
 7             if (arr == null || arr.Length == 0)
 8                 return;
 9             for (int i = 0; i < arr.Length - 1; i++) {
10                 for (int j = arr.Length - 1; j >i; j--)
11                 {
12                     if (arr[j] < arr[j - 1]) {
13                         swap(arr, j - 1, j);
14                     }
15                 }
16             }
17         }
18 
19         public static void swap(int[] arr, int i, int j) {
20             int temp = arr[i];
21             arr[i] = arr[j];
22             arr[j] = temp;
23         }

View Code

 1 /*
 2          * @Description:<p>选择排序算法实现</p>
 3          * @time:2016/03/29 下午14:42
 4          */
 5 
 6         public static void selectSort(int[] arr) {
 7             if (arr == null || arr.Length == 0)
 8                 return;
 9             int minIndex = 0;
10             for (int i = 0; i < arr.Length - 1; i++) { //只需要比较n-1次 
11                 minIndex = i;
12                 for (int j = i + 1; j < arr.Length; j++) { //从i+1开始比较，因为minIndex默认为i了,i就没必要比了。
13                     if (arr[j] < arr[minIndex]) {
14                         minIndex = j;
15                     }
16                 }
17                 if (minIndex != i) { //如果minIndex不为i,说明找到了更小的值，交换之。
18                     swap(arr, i, minIndex);
19                 
20                 }
21             }
22            
23         }
24 
25         public static void swap(int[] arr, int i, int j) {
26             int temp = arr[i];
27             arr[i] = arr[j];
28             arr[j] = temp;
29         }

View Code

插入排序算法

 1  public static void insertSort(int[] arr) {
 2             if (arr == null || arr.Length == 0)
 3                 return;
 4             for (int i = 1; i < arr.Length; i++) {//假设第一个数位置正确的；要往后移，必须要假设第一个 
 5                 int j = i;
 6                 int target = arr[i];  //待插入的
 7 
 8                 //后移
 9                 while (j > 0 && target < arr[j - 1]) {
10                     arr[j] = arr[j - 1];
11                     j--;
12                 }
13                 //插入
14                 arr[j] = target;
15             }
16         }

View Code

 快速排序算法

 1  //一次划分
 2         public static int partition(int[] arr, int left, int right)
 3         {
 4             int pivotKey = arr[left];
 5             int pivotPointer = left;
 6 
 7             while (left < right)
 8             {
 9                 while (left < right && arr[right] >= pivotKey)
10                     right--;
11                 while (left < right && arr[left] <= pivotKey)
12                     left++;
13                 swap(arr, left, right); //把大的交换到右边，把小的交换到左边。
14             }
15             swap(arr, pivotPointer, left); //最后把pivot交换到中间
16             return left;
17 
18         }
19 
20         public static void quickSort(int[] arr, int left, int right)
21         {
22             if (left >= right)
23                 return;
24             int pivotPos = partition(arr, left, right);
25             quickSort(arr, left, pivotPos - 1);
26             quickSort(arr, pivotPos + 1, right);
27         }
28 
29         public static void sort(int[] arr)
30         {
31             if (arr == null || arr.Length == 0)
32                 return;
33             quickSort(arr, 0, arr.Length - 1);
34         }
35 
36         public static void swap(int[] arr, int left, int right)
37         {
38             int temp = arr[left];
39             arr[left] = arr[right];
40             arr[right] = temp;
41         }
42 
43 ====================================优化以上代码
44 public static int partition(int[] arr, int left, int right)
45         {
46             int pivotKey = arr[left];
47             while (left < right)
48             {
49                 while (left < right && arr[right] >= pivotKey)
50                     right--;
51                 arr[left] = arr[right]; //把小的移动到左边
52                 while (left < right && arr[left] <= pivotKey)
53                     left++;
54                 arr[right] = arr[left];//把大的移动到右边
55             }
56             arr[left] = pivotKey;   //最后把pivot赋值到中间
57             return left;
58 
59         }
60 
61         public static void quickSort(int[] arr, int left, int right)
62         {
63             if (left >= right)
64                 return;
65             int pivotPos = partition(arr, left, right);
66             quickSort(arr, left, pivotPos - 1);
67             quickSort(arr, pivotPos + 1, right);
68         }
69         public static void sort(int[] arr)
70         {
71             if (arr == null || arr.Length == 0)
72                 return;
73             quickSort(arr, 0, arr.Length - 1);
74         }

View Code

 希尔排序

 1  static void Main(string[] args)
 2         {
 3             int[] arr={1,22,32,13,35,42,48,55};
 4             shellSort(arr);
 5             for (int i = 0; i < arr.Length; i++)
 6             {
 7                 Console.Write("{0},", arr[i]);
 8             }
 9             Console.ReadLine();
10         }
11 
12         public static void shellInsert(int[] arr, int d) {
13             for (int i = d; i < arr.Length; i++) {
14                 int j = i - d;
15                 int temp = arr[i];  //记录要插入的数据
16                 while (j >= 0 && arr[j] > temp) {   //从后向前，找到比其小的数的位置 
17                     arr[j + d] = arr[j];    //向后挪动
18                     j -= d;
19                 }
20 
21                 if (j != i - d)  //存在比其小的数
22                     arr[j + d] = temp;
23 
24             }
25         }
26         public static void shellSort(int[] arr) {
27             if (arr == null || arr.Length == 0)
28                 return;
29             int d = arr.Length / 2;
30             while (d >= 1) {
31                 shellInsert(arr, d);
32                 d /= 2;
33             }
34         }

View Code

归并排序

 1         static void Main(string[] args)
 2         {
 3             int[] arr={1,22,32,13,35,42,48,55};
 4             mergeSort(arr);
 5             for (int i = 0; i < arr.Length; i++)
 6             {
 7                 Console.Write("{0},", arr[i]);
 8             }
 9             Console.ReadLine();
10         }
11 
12         public static void mergeSort(int[] arr) {
13             mSort(arr, 0, arr.Length - 1);
14         }
15 
16         public static void mSort(int[] arr, int left, int right) {
17             if (left >= right)
18                 return;
19             int mid = (left + right) / 2;
20 
21             mSort(arr, left, mid);
22             mSort(arr, mid + 1, right);
23             merge(arr, left, mid, right);
24         }
25 
26         public static void merge(int[] arr, int left, int mid, int right) { 
27             //[left,mid][mid+1,right]
28             int[] temp = new int[right - left + 1];
29 
30             int i = left;
31             int j = mid + 1;
32             int k = 0;
33             while (i <= mid && j <= right) {
34                 if (arr[i] <= arr[j])
35                 {
36                     temp[k++] = arr[i++];
37                 }
38                 else {
39                     temp[k++] = arr[j++];
40                 }
41             }
42 
43             while (i <= mid) {
44                 temp[k++] = arr[i++];
45             }
46 
47             while (j <= right) {
48                 temp[k++] = arr[j++];
49             }
50 
51             for (int p = 0; p < temp.Length; p++) {
52                 arr[left + p] = temp[p];
53             }
54 
55         }

View Code