ArrayUtils.java

package iensen;

import java.util.Random;

/**
 * Created with IntelliJ IDEA.
 * User: iensen
 * Date: 2/24/13
 * Time: 10:15 AM
 * To change this template use File | Settings | File Templates.
 */
public class ArrayUtils
{
        public static void shuffle(Object[] a) {
            int n = a.length;
            Random random = new Random();

            for (int i = 0; i < n; i++) {
                int change = i + random.nextInt(n - i);
                swap(a, i, change);
            }
        }

        private static void swap(Object[] a, int i, int changeIdx) {
            Object temp = a[i];
            a[i] = a[changeIdx];
            a[changeIdx] = temp;
        }


    public static int lower_bound(Comparable[] arr, Comparable key) {
        int len = arr.length;
        int lo = 0;
        int hi = len-1;
        int mid = (lo + hi)/2;
        while (true) {
            int cmp = arr[mid].compareTo(key);
            if (cmp == 0 || cmp > 0) {
                hi = mid-1;
                if (hi < lo)
                    return mid;
            } else {
                lo = mid+1;
                if (hi < lo)
                    return mid<len-1?mid+1:-1;
            }
            mid = (lo + hi)/2;
        }
    }

    public static int upper_bound(Comparable[] arr, Comparable key) {
        int len = arr.length;
        int lo = 0;
        int hi = len-1;
        int mid = (lo + hi)/2;
        while (true) {
            int cmp = arr[mid].compareTo(key);
            if (cmp == 0 || cmp < 0) {
                lo = mid+1;
                if (hi < lo)
                    return mid<len-1?mid+1:-1;
            } else {
                hi = mid-1;
                if (hi < lo)
                    return mid;
            }
            mid = (lo + hi)/2;
        }
    }


    public static void reverse(int []a)
     {
      for(int i = 0; i < a.length/2; i++)
      {
        int temp = a[i];
        a[i] = a[a.length - i - 1];
        a[a.length - i - 1] = temp;
      }
     }


    boolean next_permutation(int[] p) {
        for (int a = p.length - 2; a >= 0; --a)
            if (p[a] < p[a + 1])
                for (int b = p.length - 1;; --b)
                    if (p[b] > p[a]) {
                        int t = p[a];
                        p[a] = p[b];
                        p[b] = t;
                        for (++a, b = p.length - 1; a < b; ++a, --b) {
                            t = p[a];
                            p[a] = p[b];
                            p[b] = t;
                        }
                        return true;
                    }
        return false;
    }
}