LeetCode-in-Java

704. Binary Search

Easy

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.

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

Constraints:

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

Solution

public class Solution {
    public int search(int[] nums, int target) {
        int left = 0;
        int right = nums.length - 1;
        if (target < nums[left] || target > nums[right]) {
            return -1;
        }
        if (nums[left] == target) {
            return left;
        } else if (nums[right] == target) {
            return right;
        }
        while (left <= right) {
            int mid = left + (right - left) / 2;
            if (target == nums[mid]) {
                return mid;
            } else if (target > nums[mid]) {
                left = mid + 1;
            } else {
                right = mid - 1;
            }
        }
        return -1;
    }
}

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