leetcode704--Binary Search

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].

想法：一般的二分法查找步骤

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