算法 - 二分查找

直接上代码：递归和while版本

public class BinarySearch<T extends Comparable> {

    /**
     * 递归二分查找
     *
     * @param arr    数组
     * @param left   左标
     * @param right  右标
     * @param target 查找值
     * @return 找到返回下标，未找到返回-1
     */
    public int binarySearch(T[] arr, int left, int right, T target) {
        if (right < left) {
            return -1;
        }
        int middle = (right - left) / 2 + left;
        if (target.compareTo(arr[middle]) == 0) {
            return middle;
        } else if (target.compareTo(arr[middle]) < 0) {
            return binarySearch(arr, left, middle - 1, target);
        } else {
            return binarySearch(arr, middle + 1, right, target);
        }
    }

    public int binarySearch(T[] arr, T target) {
        return binarySearch(arr, 0, arr.length - 1, target);
    }

    /**
     * while方式二分查找
     *
     * @param arr    数组
     * @param target 查找值
     * @return 找到返回下标，未找到返回-1
     */
    public int whileBinarySearch(T[] arr, T target) {
        int left = 0;
        int right = arr.length - 1;
        while (left <= right) {
            int middle = (right - left) / 2 + left;
            if (target.compareTo(arr[middle]) == 0) {
                return middle;
            }
            if (target.compareTo(arr[middle]) < 0) {
                right = middle - 1;
            }
            if (target.compareTo(arr[middle]) > 0) {
                left = middle + 1;
            }
        }
        return -1;
    }

    public static void main(String[] args) {
        Integer[] arr = new Integer[]{1, 2, 3, 4, 5, 6, 7, 8, 9};
        BinarySearch bs = new BinarySearch();
        System.out.println(bs.binarySearch(arr, 6));
        System.out.println(bs.binarySearch(arr, 0));
        System.out.println(bs.whileBinarySearch(arr, 11));
        System.out.println(bs.whileBinarySearch(arr, 3));
        String[] stingArr = new String[]{"A","B","B","D","E","F","G",};
        System.out.println(bs.whileBinarySearch(stingArr, "B"));
        System.out.println(bs.whileBinarySearch(stingArr, "C"));
        System.out.println(bs.binarySearch(stingArr, "G"));
    }

}