排序算法

Posted 2021-01-08 fax1996

快速排序算法

import java.util.Arrays;

public class QuickSort {
    public static void main(String[] args) {
        int[] arr = {4,5,1,9,10,5};
        quickSore(arr, 0, arr.length-1);
        System.out.println(Arrays.toString(arr));
    }
    
    public static int getIndex(int[] arr,int left,int right) {
        int key = arr[left];
        while(left<right) {
            while(arr[right]>=key&&right>left) {
                right--;
            }
            arr[left] = arr[right];
            while(arr[left]<=key&&right>left) {
                left++;
            }
        }
        arr[left] = key;
        return left;
    }
    
    public static void quickSore(int[] arr,int left,int right) {
        if(left>=right) {
            return;
        }
        int index = getIndex(arr, left, right);
        quickSore(arr, left, index-1);
        quickSore(arr, index+1, right);
    }
    
}

计数排序算法

import java.util.Arrays;

public class jiShu {
    
    public static int[] JiShu(int[] arr){
        int num =0;
        int len = arr[0];
        for(int i=1;i<arr.length;i++) {
            if(len<arr[i]) {
                len=arr[i];
            }
        }
        
        int[] arrNew = new int[len+1];
        int[] arr2 = new int[arr.length];
        
        
        for(int i=0;i<arr.length;i++) {
            arrNew[arr[i]] = arrNew[arr[i]]+1;
        }
        
        for(int i=0;i<arrNew.length;i++) {
            if(arrNew[i]>0) {
                for(int j=0;j<arrNew[i];j++) {
                    arr2[num++] =i;
                }
            }
        }
        return arr2;    
    }

    public static void main(String[] args) {
        int[] arr = {5,4,1,4,8,2};
        
        System.out.println(Arrays.toString(JiShu(arr)));
        
    }
}

二路归并排序

import java.util.Arrays;

public class testMerge {
    public static void main(String[] args) {
        int[] arr={3,1,2,5,7,5,3,8,7,6,4,8,9,34,56,78,23,12,11};
        int[] newArr=new int[arr.length];
        System.out.println(Arrays.toString(arr));
        chai(arr,0,arr.length-1,newArr);
        System.out.println(Arrays.toString(arr));
        
    }
    
    public static void chai(int[] arr,int left,int right,int[] newArr) {
        if(left>=right) {
            return;
        }else {
            //计算中间值
            int mid  = (left+right)/2;
            //递归调用
            chai(arr, left, mid, newArr);
            chai(arr, mid+1, right, newArr);
            //并
            mergeRe(arr, left, right, mid, newArr);
        }
    }
    
    
    //并
    public static void mergeRe(int[] arr,int left,int right,int mid,int[] newArr) {
        //数据集左侧的边界
        int m = left;
        int n = mid+1;
        //数据集右边的边界
        int x = mid;
        int y = right;
        //记录新数组的下标
        int index = 0;
        while(m<=x&&n<=y) {
            if(arr[m]<arr[n]) {
                newArr[index++] = arr[m++];
            }
            else {
                newArr[index++] = arr[n++];
            }
        }
        while(m<=x) {
            newArr[index++] = arr[m++];
        }
        while(n<=y) {
            newArr[index++] = arr[n++];
        }
        for(int i=0;i<index;i++) {
            arr[i+left]=newArr[i];
        }
    }

}