# 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.

## 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);
}
}
}