二进制搜索compareTo String对象

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;
    }
}

我正在发送一个包含{“ love”，“ hate”，“ happy”，“ sad”，“ neutral”}的数组，每次我尝试使用二进制搜索方法搜索“ neutral”时，它都会告诉我找不到。 是什么导致这种情况发生？

Answer 1

1. 您的输入数组必须排序才能使用二进制搜索。

2. 正如@Libby指出的那样，您的while循环需要更改以允许first小于或等于last。

3. 如果first == last时没有找到匹配项，则需要能够退出循环。

4. 如果midValue <0，则需要移动下限，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)