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));
    }

}