算法之归并排序（java、python、c++）

一、JAVA 摘录归并详细分析 ✈✈✈✈✈

package algorithm.归并;

import java.util.Arrays;

public class Fenzhi {
    public static void main(String[] args) {
        int [] arr = {8,4,1,2,7,6,3,5};
        mergeSort(arr, 0, arr.length-1, new int[8]);
        System.out.println(Arrays.toString(arr));
    }

    public static void mergeSort(int [] arr, int left, int right, int [] tmp) {
        int mid = (right + left) /2;
        if(left < right) {
            mergeSort(arr, left, mid, tmp);
            mergeSort(arr, mid+1, right, tmp);
            merge(arr, left, mid, right, tmp);
        }
    }

    public static void merge(int [] arr, int left, int mid, int right, int [] tmp) {
        int i=left;
        int j=mid + 1;
        int n=0;
        while(i<=mid && j<=right) {
            if(arr[i] <= arr[j]) {
                tmp[n] = arr[i++];
            }else{
                tmp[n] = arr[j++];
            }
            n++;
        }
        while(i<=mid) {
            tmp[n] = arr[i];
            n++;
            i++;
        }
        while(j<=right) {
            tmp[n] = arr[j];
            n++;
            j++;
        }
        int tmpleft = left;
        n = 0;
        while(tmpleft <= right) {
            arr[tmpleft] = tmp[n];
            tmpleft++;
            n++;
        }
    }
}

二、Python✈✈✈

def merge_sort(num_list):                                                                                                                                                                                                                                                 
          
      length = len(num_list)
      if length <= 1:
          return num_list
      
      mid = length // 2
  
      left_l = merge_sort(num_list[:mid])
      right_l = merge_sort(num_list[mid:])
  
      p, q, temp_list = 0, 0, list()
      
      len_left, len_right = len(left_l), len(right_l)
      
      while len_left > p and len_right > q:
          if left_l[p] <= right_l[q]:
              temp_list.append(left_l[p])
              p += 1
          else:
              temp_list.append(right_l[q])
              q += 1
      temp_list += left_l[p:]
      temp_list += right_l[q:]
  
      return temp_list
  
  if __name__ == '__main__':
      num_list = [12,33,44,13,2,1,0,-1,10]
      new_list = merge_sort(num_list)
      for k, v in enumerate(new_list):
          num_list[k] = v 
      print('num_list:',num_list)

三、C++ 借鉴文章✈✈✈✈

#include <iostream>                                                                                                                                                                                                                              
  int n, ar[20], tmp[20];
  
  void mergesort(int low, int mid, int high){
      int i=low;
      int j=high;
      n=low;
      while(i<=mid && j<= high) {
          if(ar[i]<=ar[j]){
              tmp[n++]=ar[i++];
          }else{
              tmp[n++]=ar[j++];
          }   
      }   
      while(i<=mid) {
          tmp[n++]=ar[i++];
      }   
      while(j<=high) {
          tmp[n++]=ar[j++];
      }   
      for(n=low;n<=high;n++){
          ar[n]=tmp[n];
      }   
  }
  
  void merge(int low, int high) {
      if(low>=high) return;
      int mid=(low+high)/2;
      merge(low, mid);
      merge(mid+1,high);
      mergesort(low,mid,high);
  }
  
  using namespace std;
  
  int main(){
      cin >> n;
      for(int i=1;i<=n;i++) {
          cin >> ar[i];
      }   
      merge(1, n); 
      for(int i=1;i<=n;i++) {
          cout << ar[i] << " ";    
      }   
  }

总结

• python的排序是最简单的。
  印象最深刻的就是切片语法通过【:】冒号获取前后两侧的集合。分厂方便
• c++的步骤和代码数与java很像