題目：

Given a sorted (in ascending order) integer array numsof 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].

解釋：
二分查詢經典問題。
python程式碼：

class Solution(object):
    def search(self, nums, target):
        """
        :type nums: List[int]
        :type target: int
        :rtype: int
        """
        left=0
        right=len(nums)-1
        while left<=right:
            mid=left+(right-left)/2
            if nums[mid]==target:
 

                return mid
            else:
                if nums[mid]<target:
                    left=mid+1
                else:
                    right=mid-1
        return -1

c++程式碼：

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

總結：
注意是用<=哦。