# 704.Binary Search

**704.Binary Search**

难度:Easy

> 给定一个 n 个元素有序的（升序）整型数组 nums 和一个目标值 target ，写一个函数搜索 nums 中的 target，如果目标值存在返回下标，否则返回 -1。

示例 1:

输入: nums = \[-1,0,3,5,9,12], target = 9 输出: 4 解释: 9 出现在 nums 中并且下标为 4 示例 2:

输入: nums = \[-1,0,3,5,9,12], target = 2 输出: -1 解释: 2 不存在 nums 中因此返回 -1

提示：

你可以假设 nums 中的所有元素是不重复的。 n 将在 \[1, 10000]之间。 nums 的每个元素都将在 \[-9999, 9999]之间。

二分查找，需要注意边界情况，以及循环终止条件。

```
class Solution {
public:
    int search(vector<int>& nums, int target) {
        int st=0;
        int ed=nums.size()-1;
        if(nums[st]==target) return st;
        if(nums[ed]==target) return ed;
        int mid;
        while(st <ed)
        {
            mid=(st+ed)>>1;
           if(nums[mid]==target) return mid;
            else if(nums[mid] >target)  {
                if(mid <ed)
                ed=mid;
                else return -1;
            }
                
            else 
            {
                if(mid>st)
                st=mid;
                else return -1;
            }
  //          cout<< st <<" "<< ed<<endl;
        }
        return -1;
    }
};
```

> 执行用时 :88 ms, 在所有 C++ 提交中击败了21.54%的用户\
> 内存消耗 :10.9 MB, 在所有 C++ 提交中击败了70.73%的用户


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