704. Binary Search (Easy)

Q:

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:

1. You may assume that all elements in nums are unique.
2. n will be in the range [1, 10000].
3. The value of each element in nums will be in the range [-9999, 9999].

A:

a,b is (a,b]   左闭开右开

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