面试中，BubbleSort/BinarySearch 问到的几率真高

最近在找工作，经常被问及，所以备份一下。

二分搜索：

public class BinarySearch {

    public static int search(int[] a, int key) {
	     return binarySearch(a, 0, a.length, key);
    }

    private static int binarySearch(int[] a,
         int fromIndex, int toIndex, int key) {
	int low = fromIndex;
	int high = toIndex - 1;

	while (low <= high) {
	    int mid = (low + high) >>> 1;
	    int midVal = a[mid];

	    if (midVal < key)
		low = mid + 1;
	    else if (midVal > key)
		high = mid - 1;
	    else
		return mid; // key found
	}
	return -(low + 1);  // key not found.
    }

}
//对测试Array先排序
//Arrays.sort(theArray);

冒泡：

public abstract class BubbleSorter {

    protected int length = 0;

    protected void doSort() {
        if (length <= 1)
            return;

        for (int nextToLast = length-2; nextToLast >= 0; nextToLast--)
            for (int index = 0; index <= nextToLast; index++) {
                if (outOfOrder(index))
                    swap(index);
            }
    }

    protected abstract void swap(int index);
    protected abstract boolean outOfOrder(int index);

}

public class IntBubbleSorter extends BubbleSorter {

    private int[] array = null;

    public void sort(int[] theArray) {
        array = theArray;
        length = array.length;

        doSort();
    }

    protected void swap(int index) {
        int temp = array[index];
        array[index] = array[index + 1];
        array[index + 1] = temp;
    }


    protected boolean outOfOrder(int index) {
        return (array[index] > array[index + 1]);
    }

}

BinarySearch 中常见bug：

6:             int mid =(low + high) / 2;
在一般情况下, 这个语句是不会出错的, 但是, 当low+high的值超过了最大的正int值 (2^31- 1) 的时候, mid会变成负值

那如何解决这个问题?
很简单, 修改这行语句为:

6:             int mid = low + ((high - low) / 2);
或者
6:             int mid = (low + high) >>> 1;

在c或者c++中, 则可以如下实现:
6:             mid = ((unsigned) (low + high)) >> 1;

原文：http://blog.youkuaiyun.com/longing_chen/archive/2006/06/10/785570.aspx