给定一个数组，求如果排序之后，相邻两数的最大差值，要求时 间复杂度O(N)，且要求不能用非基于比较的排序

思路：

　　桶排序

　　N个数，设置 N+ 1 个桶，，一定有一个空桶，，为的是保证最大差值一定是不是出现在同一个桶中；

　　只要比较 非空桶 的最小值，与前一个 非空桶的最大值，求 最大的差值，

 

package my_basic;

import java.text.Bidi;
import java.util.Arrays;

public class MaxGap {

    /*给定一个数组，求如果排序之后，相邻两数的最大差值，要求时 间复杂度O(N)，且要求不能用非基于比较的排序*/
    
    public static int maxGap(int[] arr) {
        if (arr == null || arr.length < 2) {
            return 0;
        }
        //获取最小值 最大值
        int len = arr.length;
        int min = Integer.MAX_VALUE;
        int max = Integer.MIN_VALUE;
        for (int i = 0; i < arr.length; i++) {
            min = Math.min(min, arr[i]);
            max = Math.max(max, arr[i]);
        }
        if (min == max) {
            return 0;
        }
        //放到桶里
        boolean[] hasNum = new boolean[len + 1];
        int[] mins = new int[len + 1];
        int[] maxs = new int[len + 1];
        
        int bid = 0;
//        for (int i = 0; i < arr.length; i++) {
//            bid = bucket(arr[i], len, min, max);
//            hasNum[bid] = true;
//            mins[bid] = Math.min(mins[bid], arr[i]);
//            maxs[bid] = Math.max(maxs[bid], arr[i]);        
//        }
        for (int i = 0; i < len; i++) {
            bid = bucket(arr[i], len, min, max);
            mins[bid] = hasNum[bid] ? Math.min(mins[bid], arr[i]) : arr[i];
            maxs[bid] = hasNum[bid] ? Math.max(maxs[bid], arr[i]) : arr[i];
            hasNum[bid] = true;
        }
        
        //找最大间距
        int res =0;
        int m = maxs[0];
        for(int i=1 ;i <= len;i++) {
            if (hasNum[i]) {
                res = (mins[i] - m)>res ? (mins[i] - m) : res;
                m = maxs[i];
            }
        }
        return res;

    }
    
    //放到几号桶里
    public static int bucket(long num, long len, long min, long max) {
        return (int) ((num - min) * len / (max - min));
    }
    
    //对数器
    public static int[] generateRandomArray(int maxSize, int maxValue) {
        int[] arr = new int[(int) ((maxSize + 1) * Math.random())];
        for (int i = 0; i < arr.length; i++) {
            arr[i] = (int) ((maxValue + 1) * Math.random()) - (int) (maxValue * Math.random());
        }
        return arr;
    }
    public static int comparetor(int[] arr) {
        if (arr==null || arr.length < 2) {
            return 0;
        }
        Arrays.sort(arr);
//        printArray(arr);
        int res=0;
        for (int i = 1; i < arr.length; i++) {
            res = (arr[i] - arr[i-1]) > res? (arr[i] - arr[i-1]) :res;
        }
        return res;
    }
    
    public static void printArray(int[] arr) {
        for (int i = 0; i < arr.length; i++) {
            System.out.print(arr[i]+" ");
        }
        System.out.println();
    }
    public static int[] copyArray(int[] arr) {
        if (arr == null) {
            return null;
        }
        int[] res = new int[arr.length];
        for (int i = 0; i < arr.length; i++) {
            res[i] = arr[i];
        }
        return res;
    }

    public static void main(String[] args) {
        int maxSize =10;
        int maxValue = 50;
        boolean succeed = true;
        int[] arr1 = generateRandomArray(maxSize, maxValue);
        printArray(arr1);        
        int res = maxGap(arr1);
        
        int[] arr2 = copyArray(arr1);
        int res2 = comparetor(arr2);
        if (res != res2) {
            printArray(arr1);
            printArray(arr2);
            System.out.println(res);
            System.out.println(res2);
            
        }else {
            System.out.println("nice!");
        }
        
    }

    

}