08. Binary Search.cpp

/*
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:
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].
*/

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