Question

class ObjectBinarySearcher{

    public static int search(String[] array, String value){

        int first = 0, last = array.length-1, position = -1;
        boolean found = false;

        while(!found && first < last){
            int mid = (first+last)/2;
            int midValue = array[mid].compareTo(value);

            if(midValue==0){
                position = mid;
                found = true;
            }
            else if(midValue<0)
                last = mid-1;
            else
                first = mid+1;
        }

        return position;
    }
}

我发送的数组包含{“love”，“hate”，“happy”，“sad”，“neutral”}，每当我尝试使用二进制搜索方法搜索“中性”时，它告诉我它没有找到。是什么导致这种情况发生？

Answer 1

必须对输入数组进行排序才能使用二进制搜索。
正如@Libby指出的那样，你的while循环需要改变为允许第一个小于或等于last。
如果first == last找不到匹配项，您需要退出循环。
如果midValue＆lt; 0你需要移动下限，而不是上限（反之亦然）。

新代码：

while (!found && first <= last) { // allow first to be lower or equal to last
    int mid = (first + last) / 2;
    int midValue = array[mid].compareTo(value);

    if (midValue == 0) { // matched!

        position = mid;
        found = true;

    } else if (first == last) { // didn't match and there was only one left to check

        break; // so break out of the loop

    } else if (midValue < 0) { // current pos is too low

        first = mid + 1; // so adjust the lower bound

    } else { // current pos is too high

        last = mid - 1; // so adjust the upper bound

    }
}

Answer 2

将while loop更改为while(!found && first <= last)

二进制搜索compareTo String对象

2 个答案: