题目

复习下快排和归并 果然忘了hhhh
快排

import java.util.*;


public class Solution {
    
    
    /**
     * 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
     * 将给定数组排序
     * @param arr int整型一维数组 待排序的数组
     * @return int整型一维数组
     */
    public int[] MySort (int[] arr) {
    
    
        quickSort(arr ,0 ,arr.length-1);
        return arr;
    }
    public void quickSort(int[] nums ,int l ,int r){
    
    
        if(l >= r) return;
        int base = nums[l];
        int i = l ,j = r;
        while(i < j){
    
    
            while(i < j && nums[j] >= base) j--;
            while(i < j && nums[i] <= base) i++;
            if(i < j){
    
    
                int temp = nums[i];
                nums[i] = nums[j];
                nums[j] = temp;
            }
        }
        nums[l] = nums[j];
        nums[j] = base;
        quickSort(nums,l,j-1);
        quickSort(nums,j+1,r);
    }
}

归并

    public int[] MySort (int[] arr) {
    
    
        mergeSort(arr ,0 ,arr.length-1);
        return arr;
    }
    public void mergeSort(int[] nums ,int l ,int r){
    
    
        if (l >= r) return;
        int mid = (l+r)/2;
        mergeSort(nums ,l ,mid);
        mergeSort(nums ,mid+1 ,r);
        merge(nums ,l ,mid ,r);
    }
    public void merge(int[] nums ,int l ,int mid ,int r){
    
    
        int[] tmp = new int[r-l+1];
        int p1 = l ,p2 = mid +1 ,k = 0;
        while (p1 <= mid && p2 <= r){
    
    
            tmp[k++] = nums[p1] < nums[p2] ? nums[p1++] : nums[p2++];
        }
        while (p1 <= mid){
    
    
            tmp[k++] = nums[p1++];
        }
        while (p2 <= r){
    
    
            tmp[k++] = nums[p2++];
        }
        for (int i = 0; i < tmp.length; i++) {
    
    
            nums[l+i] = tmp[i];
        }
    }