以二分查找算法为基础实现二分插入答案

【问题标题】：Using a binary search algorithm as a basis to implement a binary insert以二分查找算法为基础实现二分插入
【发布时间】：2012-08-31 07:47:23
【问题描述】：

我正在尝试实现二进制插入方法。

目前这个方法很简单，它接受一个参数，在一个while循环中它搜索一个比参数大的元素（在这种情况下是一个人的姓氏的字符串），一旦它中断找到它并将数组的其余部分向右移动。然后将参数插入到break的位置。

我尝试将其更改为通过借用二进制搜索算法来搜索插入位置的方法。但是，我就是无法让它工作。

你能告诉我我做错了什么吗？这是我的代码：

公共无效插入（个人） {

    String lastName = person.getLastName();

    int position = -1; // the position from which the array will be shifted to the right and where the argument will be inserted, will be assigned properly below

    int lowerBound = 0;
    int upperBound = numElems - 1;
    int currIt;

    if (numElems == 0)
        array[0] = person; // if array empty insert at first position
    else 
    {
        while (true) 
        {
            currIt = (lowerBound + upperBound) / 2; //the item to compare with

            int result2 = 0;

            int result1 = array[currIt].getLastName().compareTo(lastName);

            if (array[currIt+1] != null) // if the next element is not null, compare the argument to it
                result2 = array[currIt+1].getLastName().compareTo(lastName);

            if (currIt == 0 && result1 > 0) // this is when the argument is smaller then the first array element
            { 
                position = 0;
                break;
            }
            // if the position to insert is the last one, or we have found a suitable position between a smaller and a bigger element
            else if (  (result1 < 0 && (currIt == numElems-1))  ||  (result1 < 0 && result2 > 0)  ) {
                position = currIt+1;             
                break;
            }    
            else
            {
                if (result1 < 0)  // the place to put it should be in the upper half
                    lowerBound = currIt + 1; 
                else 
                    upperBound = currIt - 1; //in the lower half              
            }

        }
    }
    // position has been set to anything else other -1, then we have found our spot, probably a redundant check but useful for debugging
    if (position != -1)
    {
        //shift array to the right and insert element
        for (int j = numElems; j > position; j--)
        array[j] = array[j-1];
        System.out.println("Inserted an element");
        array[position] = person;
        numElems++;
    }

}

【问题讨论】：

你能提供一个最简单的例子来说明你的问题吗？
如果说我们有以下内容：arr.insert(new Person("Charles", "Dickens", 23));arr.insert(new Person("Adam", "Bay", 29)); arr.insert(new Person("Ethan", "Fowler", 18)); 我希望按姓氏排列它们（“Bay”...）；这很好用：String lastName = person.getLastName(); int i; for (i = 0; i < numElems; i++) if (array[i].getLastName().compareTo(lastName) > 0) break; for (int j = numElems; j > i; j--) array[j] = array[j-1]; array[i] = person; numElems++; 但想加快速度:)

标签： java arrays insert binary sorted

【解决方案1】：

您的“可能 [] 冗余检查”禁止初始插入。位置第一次是-1。

在顶部将position 设置为0，应该可以解决问题。

【讨论】：