Java big data platform development study notes (12)-merge sort

1. Data structure and algorithm:

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1.1. Create a merge sort method:

 public static void mergerSort(int[] arr, int left, int right, int[] temp) {
    
    
     if(left < right) {
    
    
         int mid = (left+right) / 2;
         mergerSort(arr, left, mid, temp);
         mergerSort(arr, mid+1, right, temp);
         merger(arr, left, mid, right, temp);
     }
 }
 

1.2. Create a merge method for merge sort:

 public static void merger(int[] arr, int left, int mid, int right, int[] temp){
    
    
     int i = left;
     int j = mid + 1;
     int t = 0;

     while(i<=mid && j<=right){
    
    
         if(arr[i] <= arr[j]){
    
    
             temp[t] = arr[i];
             t++;
             i++;
         }else{
    
    
             temp[t] = arr[j];
             t++;
             j++;
         }
     }
     while(i <= mid){
    
    
         temp[t] = arr[i];
         t++;
         i++;
     }
     while(j <= right){
    
    
         temp[t] = arr[j];
         t++;
         j++;
     }

     t=0;
     int tempLeft = left;
     while(tempLeft <= right){
    
    
         arr[tempLeft] = temp[t];
         t++;
         tempLeft++;
     }
 }
 

1.3, main method:

public static void main(String[] args) {
    
    
     //随机创建8万 个数据
     int arr[]= new int[80000];
     int temp[] = new int[arr.length];
     for(int i=0; i<arr.length; i++){
    
    
         arr[i] = (int)(Math.random()*80000);
     }
     //计算 冒泡排序时间
     double start = System.currentTimeMillis();
     System.out.println("计时开始：");
     mergerSort(arr,0, arr.length-1, temp);//此处写要测试的代码
     double end = System.currentTimeMillis();
     System.out.println("计时结束, 共耗时:"+ (double)((end-start)/1000) +"秒");
}
    

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• Written by ChiKong_Tam on September 10, 2020