选择排序

选择排序

时间复杂度为O(n^2)
import java.util.Arrays;

public class Code_02_SelectionSort {
        public static void selectionSort(int []arr){
            if(arr==null||arr.length<2){
                return;
            }
            for(int i=0;i<arr.length-1;i++){
                int minIndex=i;
                for(int j=i+1;j<arr.length;j++){
                    minIndex=arr[j]<arr[minIndex]?j : minIndex;
                }
                swap(arr,i,minIndex);
            }
        }

    private static void swap(int[] arr, int i, int j) {

          int temp=arr[i];
            arr[i]=arr[j];
            arr[j]=temp;
            /*
            java这样为什么会出错?
            arr[i]+=arr[j];
            arr[j]=a[i]-arr[j];
            arr[j]=arr[i]-arr[j];
            */
    }

    //for test
    public static void comparator(int []arr){
            Arrays.sort(arr);
    }

    //for test
    public static int []generateRandomArray(int maxSize,int maxValue){
            int []arr=new int[(int)((maxSize+1)*Math.random())];
        for (int i = 0; i < arr.length; i++) {
            arr[i]=(int)((maxValue+1)*Math.random())-(int)((maxValue)*Math.random());

        }
        return arr;
    }
    //for test
    public static int[]copyArray(int []arr){
            if(arr==null){
                return null;
            }
            int []res=new int[arr.length];
        for (int i = 0; i < arr.length; i++) {
            res[i]=arr[i];

        }
        return res;
    }
    //for test
    public static boolean isEqual(int []arr1,int []arr2 ){
            if((arr1==null&&arr2!=null)||(arr1!=null&&arr2==null)){
                return false;
            }
            if (arr1==null&&arr2==null){
                return true;
            }
            if(arr1.length!=arr2.length){
                return false;
            }
        for (int i = 0; i < arr1.length; i++) {
            if(arr1[i]!=arr2[i]){
                return false;
            }

        }
        return true;

    }
    //for test
    public static void printArray(int []arr){
            if (arr==null){
                return;
            }
        for (int i = 0; i < arr.length; i++) {
            System.out.print(arr[i]+" ");

        }
        System.out.println();
    }

    public static void main(String[] args) {
        int testTime=5000000;
        int maxSize=100;
        int maxValue=100;
        boolean succeed=true;
        for (int i = 0; i < testTime; i++) {
            int []arr1=generateRandomArray(maxSize,maxValue);
            int []arr2=copyArray(arr1);
            selectionSort(arr1);
            comparator(arr2);
            if(!isEqual(arr1,arr2)){
                succeed=false;
                printArray(arr1);
                printArray(arr2);
                break;
            }

        }
        System.out.println(succeed?"Nice !":"Fucking fucked !");
        int []arr=generateRandomArray(maxSize,maxValue);
        printArray(arr);
        selectionSort(arr);
        printArray(arr);


    }


}

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