java - 二分查找条件

Question

<分区>

Answer 1

1. while (low < high)在搜索范围 [low, high) 时使用.更新时 high , 使用 high = mid .更新时 low , 使用 low = mid + 1 .
2. while (high - low > 1)在搜索范围 (low, high) 时使用.更新时 high , 使用 high = mid .更新时 low , 使用 low = mid .
3. while (low <= high)在搜索范围 [low, high] 时使用.更新时 high , 使用 high = mid - 1 .更新时 low , 使用 low = mid + 1 .

代码如下:

public class BinarySearch {
    public static void main(String[] args) {
        Integer[] nums = { 4, 9, 12, 18, 20, 26, 28, 29, 55 };

        for (int i = 0; i < nums.length; ++i) {
            System.out.println(binarySearch1(nums, nums[i]));
            System.out.println(binarySearch2(nums, nums[i]));
            System.out.println(binarySearch3(nums, nums[i]));
        }
    }

    public static <T extends Comparable<T>> int binarySearch1(T[] array, T value) {
        final int NOT_FOUND = -1;
        int low = 0;
        int high = array.length;

        while (low < high) {
            int mid = low + (high - low) / 2;
            int comparison = array[mid].compareTo(value);

            if (comparison == 0) {
                return mid;
            } else if (comparison > 0) {
                high = mid;
            } else {
                low = mid + 1;
            }
        }

        return NOT_FOUND;
    }

    public static <T extends Comparable<T>> int binarySearch2(T[] array, T value) {
        final int NOT_FOUND = -1;
        int low = -1;
        int high = array.length;

        while (high - low > 1) {
            int mid = low + (high - low) / 2;
            int comparison = array[mid].compareTo(value);

            if (comparison == 0) {
                return mid;
            } else if (comparison > 0) {
                high = mid;
            } else {
                low = mid;
            }
        }

        return NOT_FOUND;
    }

    public static <T extends Comparable<T>> int binarySearch3(T[] array, T value) {
        final int NOT_FOUND = -1;
        int low = 0;
        int high = array.length - 1;

        while (low <= high) {
            int mid = low + (high - low) / 2;
            int comparison = array[mid].compareTo(value);

            if (comparison == 0) {
                return mid;
            } else if (comparison > 0) {
                high = mid - 1;
            } else {
                low = mid + 1;
            }
        }

        return NOT_FOUND;
    }
}