Binary Search
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.
思路一：二分查找，注意边界条件
public int search(int[] nums, int target) {
int low = 0;
int high = nums.length - 1;
while (low <= high) {
int mid = (low + high) >> 1;
if (target > nums[mid]) {
low = mid + 1;
} else if (target < nums[mid]) {
high = mid - 1;
} else {
return mid;
}
}
return -1;
}