二分查找

 

    /**
     * 存在则返回下标，反之则返回-1
     * @param arr
     * @param target
     * @return
     */
    public int binarySearch(int[] arr, int target) {
        int low = 0;
        int high = arr.length - 1;
        while (low <= high) {
            int mid = (low + high) / 2;
            if (target == arr[mid]) {
                return mid;
            } else if (target < arr[mid]) {
                high = mid - 1;
            } else {
                low = mid + 1;
            }
        }
        return -1;
    }