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Binary Search

Tags : binary-search, array, leetcode, cpp, easy

Problem Statement - link #

Given an array of integers nums which is sorted in ascending order, and an integer target, write a function to search target in nums. If target exists, then return its index. Otherwise, return -1.

You must write an algorithm with O(log n) runtime complexity.

Examples #

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

Constraints #

Solution #

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