704. Binary Search

1. Questions

Given an array of integers nums which is sorted in ascending order, and an integer target, write a function to search target in nums. If target exists, then return its index. Otherwise, return -1.

You must write an algorithm with O(log n) runtime complexity.

2. Examples

Example 1:

Input: nums = [-1,0,3,5,9,12], target = 9
Output: 4
Explanation: 9 exists in nums and its index is 4

Example 2:

Input: nums = [-1,0,3,5,9,12], target = 2
Output: -1
Explanation: 2 does not exist in nums so return -1

3. Constraints

• 1 <= nums.length <= 10⁴
• -10⁴ < nums[i], target < 10⁴
• All the integers in nums are unique.
• nums is sorted in ascending order.

4. References

来源：力扣（LeetCode） 链接：https://leetcode-cn.com/problems/binary-search 著作权归领扣网络所有。商业转载请联系官方授权，非商业转载请注明出处。

5. Solutions

class Solution {
    public int search(int[] nums, int target) {
        return binarySearch(0, nums.length - 1, nums, target);
    }

    public int binarySearch(int left, int right, int[] nums, int target) {
        if (left >= right && nums[left] != target) {
            return -1;
        }
        int mid = (right + left) / 2;
        if (nums[mid] == target) {
            return mid;
        } else if (nums[mid] > target) {
            return binarySearch(left, mid, nums, target);
        } else {
            return binarySearch(mid + 1, right, nums, target);
        }
    }
}