Description
Given a sorted (in ascending order) integer array nums
of n
elements and a target
value, write a function to search target
in nums
. If target
exists, then return its index, otherwise return -1
.
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
Note:
- You may assume that all elements in
nums
are unique. - n will be in the range
[1, 10000]
. - The value of each element in
nums
will be in the range[-9999, 9999]
.
Analyse
从一个list里找出一个数,不存在则返回-1
使用二分查找,每次将问题的规模减半
int search(vector<int>& nums, int target)
{
int left = 0;
int right = nums.size() - 1;
int mid = (left + right) / 2;
while (left <= right)
{
if (nums[mid] == target)
{
return mid;
}
else if (nums[mid] > target)
{
right = mid - 1;
}
else if (nums[mid] < target)
{
left = mid + 1;
}
mid = (left + right) / 2;
}
return -1;
}