Groupon面经Prepare: Sort given a range && Summary: Bucket Sort

首先是如何sort一个只有0和1的数组，要求inplace. follow up是告诉一个range，如何在O(N)时间内sort好

两个pointer可解

 package Sorting;
 import java.util.*;

 public class InplaceSorting {
     public void sorting(int[] arr) {
         if (arr==null || arr.length==0) return;
         int l=0, r=arr.length-1;
         while (l < r) {
             while (l<r && arr[l]==0) {
                 l++;
             }
             while (l<r && arr[r]==1) {
                 r--;
             }
             if (l == r) return;
             swap(arr, l, r);
         }
     }

     public void swap(int[] arr, int l, int r) {
         int temp = arr[l];
         arr[l] = arr[r];
         arr[r] = temp;
     }

     /**
      * @param args
      */
     public static void main(String[] args) {
         // TODO Auto-generated method stub
         InplaceSorting sol = new InplaceSorting();
         int[] arr = new int[]{0,1,1,0,1,0,0,1};
         sol.sorting(arr);
         System.out.println(Arrays.toString(arr));
     }

 }

BucketSort可解

Best case performance: O(n + k), where k is the size of buckets or the range between min and max in original array

Worst case performance: O(n^2)

Aver case performance: O(n + k)

Worst case space: O(n*k)

BucketSort works as follows:

1. set up an array of initially empty buckets(should know the range)

2. Go over the original array, put each object in its bucket

3. Sort each non-empty bucket.

4. visit the buckets in order and put all elements back into the original array.

 package Sorting;

 import java.util.Arrays;

 public class Solution {
     public void bucketSort(int[] arr, int min, int max) {
         int[] bucket = new int[max-min+1];
         for (int elem : arr) {
             bucket[elem-min]++;
         }
         int cur = 0;
         for (int i=0; i<bucket.length; i++) {
             while (bucket[i] > 0) {
                 arr[cur++] = i+min;
                 bucket[i]--;
             }
         }
     }

     /**
      * @param args
      */
     public static void main(String[] args) {
         // TODO Auto-generated method stub
         Solution sol = new Solution();
         int[] arr = new int[]{5,6,9,10,4,11,5,7,6,11};
         sol.bucketSort(arr, 4, 11);
         System.out.println(Arrays.toString(arr));
     }

 }