java 实现计数排序和桶排序实例代码

public static int[] countSort1(int[] arr){
  if (arr == null || arr.length == 0) {
    return null;
  }
  
  int max = Integer.MIN_VALUE;
  int min = Integer.MAX_VALUE;
  
  //找出数组中的最大最小值
  for(int i = 0; i < arr.length; i++){
    max = Math.max(max, arr[i]);
    min = Math.min(min, arr[i]);
  }
  
  int help[] = new int[max];
  
  //找出每个数字出现的次数
  for(int i = 0; i < arr.length; i++){
    int mapPos = arr[i] - min;
    help[mapPos]++;
  }
  
  int index = 0;
  for(int i = 0; i < help.length; i++){
    while(help[i]-- > 0){
      arr[index++] = i+min;
    }
  }
  
  return arr;
}

public static int[] countSort2(int[] arr){
  int max = Integer.MIN_VALUE;
  int min = Integer.MAX_VALUE;
  
  //找出数组中的最大最小值
  for(int i = 0; i < arr.length; i++){
    max = Math.max(max, arr[i]);
    min = Math.min(min, arr[i]);
  }
  
  int[] help = new int[max - min + 1];
  
  //找出每个数字出现的次数
  for(int i = 0; i < arr.length; i++){
    int mapPos = arr[i] - min;
    help[mapPos]++;
  }
  
  //计算每个数字应该在排序后数组中应该处于的位置
  for(int i = 1; i < help.length; i++){
    help[i] = help[i-1] + help[i];
  }
  
  //根据help数组进行排序
  int res[] = new int[arr.length];
  for(int i = 0; i < arr.length; i++){
    int post = --help[arr[i] - min];
    res[post] = arr[i];
  }
  
  return res;
}

public static void bucketSort(int[] arr){
  
  int max = Integer.MIN_VALUE;
  int min = Integer.MAX_VALUE;
  for(int i = 0; i < arr.length; i++){
    max = Math.max(max, arr[i]);
    min = Math.min(min, arr[i]);
  }
  
  //桶数
  int bucketNum = (max - min) / arr.length + 1;
  ArrayList<ArrayList<Integer>> bucketArr = new ArrayList<>(bucketNum);
  for(int i = 0; i < bucketNum; i++){
    bucketArr.add(new ArrayList<Integer>());
  }
  
  //将每个元素放入桶
  for(int i = 0; i < arr.length; i++){
    int num = (arr[i] - min) / (arr.length);
    bucketArr.get(num).add(arr[i]);
  }
  
  //对每个桶进行排序
  for(int i = 0; i < bucketArr.size(); i++){
    Collections.sort(bucketArr.get(i));
  }
  
  System.out.println(bucketArr.toString());
  
}